Bring a large pot of salted water to boil.: The steam will smell clean and slightly metallic as the water reaches a rolling boil, and you will hear a lively bubbling sound. Salting the water is essential because it seasons the spaghetti from the inside out, enhancing the final dish, so aim for the water to taste slightly like the sea. A common mistake is under salting, which results in flat tasting pasta, so be generous but not excessive. Use a pot large enough that the pasta can move freely, this prevents sticking and ensures even cooking.
Trim the broccoli rabe stems, removing the thick bottom third. Remove any leaves from the stalk - you can leave some towards the top. Roughly chop the cleaned rabe into 1-inch pieces.: As you trim, the greens release a fresh, earthy scent and the stems reveal a firmer, vegetal snap when bent. Keeping the tender leaves and removing the woody bottoms balances texture, ensuring the thicker stems become tender without the leaves turning to mush. Avoid cutting the pieces too small, or they will disintegrate into the pasta; conversely, leaving them too large can make biting awkward. Consistent size helps even cooking and a pleasant mouthfeel.
Cook the spaghetti according to package directions. 3 minutes before al dente, add the broccoli to the pot.: The water will roar when you add the spaghetti , and later you will notice the pasta surface become slightly glossy as the starch releases. Adding the broccoli rabe three minutes before the end allows the stems to soften while the leaves keep their color and bite. This technique fuses the cooking steps and reduces dishes, which I prefer on busy nights. A frequent error is adding the greens too early, which makes them limp and dull in color; time them so they remain lively.
When the pasta is cooked to your liking, drain the pot in a colander in the sink and shake it to remove any excess water.: As you lift the colander, you will see steam rising and hear the faint drip of hot water, while the pasta glistens with a light starch sheen. Give the colander a gentle shake to remove excess water but do not rinse, because the pasta surface needs the residual starch to bind with the sundried tomato paste and pecorino cheese . A common slip is rinsing the pasta, which strips flavor and prevents the sauce from adhering properly, so avoid that. Let the residual moisture remain; it helps create a cohesive sauce when tossed.
Toss the cooked pasta and rabe with the tomato paste, half of the pecorino, and a drizzle of olive oil (if necessary). Taste for seasoning and add salt and pepper as necessary. Divide between two bowls and garnish with the remaining cheese.: Here you will smell the concentrated tomato and feel the glossy finish as you fold everything together. The paste should break up and cling to the strands, while the pecorino cheese begins to melt and lend a creamy, savory lift. Use moderate force when tossing so the ingredients combine evenly without bruising the greens. If the mixture seems dry, add a touch more Olive oil or a tablespoon of reserved pasta water to loosen it. A misstep is adding too much oil at once, which can make the dish greasy; instead, add gradually until you reach a silky coating. Taste and add salt and pepper as necessary, then divide between bowls and garnish with the remaining cheese so each serving has a bright finish.