Bring a large pot of salted water to a boil. Add the pasta and cook according to package directions until al dente. Just before draining, remove 1 1/2 cups of the pasta cooking water. Drain. Heat 2 tablespoons olive oil in a large skillet over high heat. When the oil shimmers, add the chicken sausage and brown all over, about 5 to 8 minutes. Reduce the heat to low, add the shallots, garlic, oregano, thyme and a pinch of red pepper flakes. Cook until the shallots begin to caramelize, about 5 minutes. Stir in the tomato paste, cook 2 minutes. Stir in the crushed tomatoes, 1 cup pasta cooking water, and season with salt and pepper. Simmer for 10-15 minutes or until the sauce thickens slightly. Add the greens, stirring until wilted. Taste and adjust seasonings as needed. Add the pasta shells and 1/2 cup basil, tossing to combine. If needed, thin the sauce with additional pasta cooking water. In a small bowl, mix the remaining 1/4 cup olive oil with the remaining 1/2 cup basil, lemon zest, lemon juice, and a pinch of salt. Spread the ricotta cheese into the bottom of each pasta bowl. Spoon the shells and sauce over the ricotta. Drizzle the basil lemon sauce overtop. Serve and enjoy!: The smell of heavily salted boiling water reminds me of the sea, and it is crucial because properly seasoned water flavors the pasta shells from the inside out. You want the water to be vigorously boiling so the shells move freely, avoiding sticking. A common mistake is under salting the water, which results in bland pasta; aim for water that tastes like the sea. Keep an eye on the pot, because once boiling, water can foam up quickly.
Add the pasta and cook according to package directions until al dente: When the shells are al dente, they should give slightly when bitten, offering pleasant tooth rather than floppiness. The texture will finish cooking a bit when tossed with the sauce, so err toward slightly firmer than you would eat solo. Overcooked shells become mushy and tear when tossed, so set a timer and start tasting a minute or two before the package time.
Just before draining, remove 1 1/2 cups of the pasta cooking water: This starchy, hot pasta water is a secret helper that emulsifies and thins the sauce while adding cohesion. Scoop it carefully into a heatproof measuring cup so you have it on hand. A frequent slip is not reserving enough water, which can leave the sauce too thick; rescue this by adding small amounts until you get a glossy finish.
Drain: As you drain the shells, notice how they look glossy and plump rather than lifeless; that shine is a good sign. Drain promptly to stop cooking and prevent them from becoming waterlogged. Avoid rinsing, rinsing washes away surface starch that helps the sauce cling.
Heat 2 tablespoons olive oil in a large skillet over high heat: When the oil shimmers and moves easily, it is hot enough to brown the sausage and create flavorful fond. You want immediate sizzle on contact; if the oil smokes, lower the heat, because burnt oil will taint the dish. Using the right heat ensures caramelization which builds depth.
When the oil shimmers, add the chicken sausage and brown all over, about 5 to 8 minutes: Browning creates those tasty browned bits that dissolve into the sauce and intensify savory flavors. Listen for a lively sizzle and watch for golden edges; move the meat occasionally so it browns evenly. A trap is overcrowding the pan, which causes steaming and prevents proper browning, so brown in batches if needed.
Reduce the heat to low, add the shallots, garlic, oregano, thyme and a pinch of red pepper flakes: Lowering the heat lets the shallots and garlic soften without burning, releasing sweetness and fragrant oils. Stir gently until the shallots begin to caramelize and the herbs smell toasty. Burnt garlic will taste acrid, so add it after the shallots have softened to avoid that bitter note.
Cook until the shallots begin to caramelize, about 5 minutes: Caramelization brings a honeyed complexity to the sauce; you should see edges turning golden and smell a deep, sweet aroma. Gentle heat and patience are key here, as rushing will keep the shallots raw and sharp. Stir occasionally to avoid uneven browning and to coax out natural sugars.
Stir in the tomato paste, cook 2 minutes: Heating the tomato paste in the pan deepens its flavor and removes rawness, creating richer, more rounded tomato notes. It will darken slightly and cling to the pan, which is perfect for building the sauce base. Don’t skip this step, as raw paste tastes flat and one dimensional.
Stir in the crushed tomatoes, 1 cup pasta cooking water, and season with salt and pepper: Adding crushed tomatoes and reserved starchy water creates a luscious, integrated sauce. The pasta water helps bind oil and tomato into a silky emulsion while adding body. Taste and adjust salt and pepper now, because the sauce will concentrate as it simmers; adjust gradually to avoid over seasoning.
Simmer for 10 to 15 minutes or until the sauce thickens slightly: As the sauce simmers, aromas will intensify and flavors will meld into a cohesive whole. Look for gentle bubbling and a slightly reduced volume, with the sauce coating the back of a spoon. If it reduces too far and becomes pasty, stir in more reserved pasta water slowly until the texture is glossy and saucy again.
Add the greens, stirring until wilted: Stirring in chopped greens at this point lets them wilt into the sauce, contributing color and an earthy note. They will release some moisture, which also helps loosen the sauce. Overcooking makes greens lifeless and gray, so remove from heat as soon as they are tender and vibrant.
Taste and adjust seasonings as needed: Now is the moment to balance acidity, salt, and heat. A pinch more salt or a squeeze more lemon juice can elevate the entire dish. Avoid adding too much at once; small adjustments keep the sauce harmonious without overpowering one element.
Add the pasta shells and 1/2 cup basil, tossing to combine: Tossing combines textures so the shells carry sauce into every bite, and the added chopped basil releases fresh aromatics that brighten the finished plate. Use tongs to gently fold so shells remain intact. If the sauce seems dry, add reserved pasta water a tablespoon at a time until the coating is satiny and even.
If needed, thin the sauce with additional pasta cooking water: The final texture should be glossy and cling to shells, not pool separately. Adding hot starchy water is the safest way to adjust consistency without diluting flavor. A common misstep is adding plain water which waters down taste, so always use pasta water for thinning.
In a small bowl, mix the remaining 1/4 cup olive oil with the remaining 1/2 cup basil, lemon zest, lemon juice, and a pinch of salt: This basil lemon oil is an aromatic finishing touch, and its bright acidity awakens the entire dish. Whisk until emulsified and taste for balance, adding salt sparingly. If the lemon is too forward, a little more oil softens it while preserving brightness.
Spread the ricotta cheese into the bottom of each pasta bowl: The cool whipped ricotta forms a creamy base that contrasts temperature and texture, making the dish feel elevated. Smooth it into a shallow bed so the warm shells sit on top and melt slightly into it. Be gentle to keep bowls neat and inviting.
Spoon the shells and sauce over the ricotta: As you plate, notice the way steam rises and mingles with the basil oil aroma, signaling a ready dish. The warm sauce ripples over the cool ricotta, creating a luxurious mouthfeel. Plate with care so each serving looks abundant yet balanced.
Drizzle the basil lemon sauce overtop: The final drizzle adds a bright, herbal finish and a glossy sheen. It should perfume the dish without overwhelming the tomato sauce, so a light hand produces the best results. If you overdo it, the lemon can dominate, so taste as you go.
Serve and enjoy: This is the reward for careful seasoning and timing, when textures, heat, and brightness are in harmony. Encourage guests to scrape the bowl to get all the ricotta and sauce together, that is part of the joy. If a plate tastes unbalanced, a pinch of salt or a squeeze of lemon can quickly rescue it at the table.