In a 12-inch skillet add butter and set over medium-high heat.: As the butter melts it will foam and release a rich, nutty aroma, signaling that it is ready for the next ingredient. You should hear a gentle sizzle as the butter hits the pan, which means the surface is hot enough to brown the mushrooms. Getting the skillet to the right temperature matters because it creates those caramelized edges that concentrate flavor. A common mistake is starting with too low heat, which causes the mushrooms to sweat and become soggy rather than golden. If the butter begins to brown too quickly, lower the heat and let it settle; the goal is a warm, foaming sheen, not a dark scorch.
When the butter has fully melted add the mushrooms, shallots, and thyme leaves. Saute for about 10 minutes or until the mushrooms are soft and slightly browned.: Right after adding the wild mushrooms , you should hear a louder sizzle as moisture meets the hot fat, and the pan will start to release an earthy steam that smells very savory. The shallot will begin to soften and sweeten, blending with the thyme as it warms. Spread the mushrooms so they are in a single layer as much as possible, because contact with the hot surface encourages browning instead of steaming. Overcrowding is a frequent error that results in limp, gray mushrooms; if your pan is small, cook in batches to achieve deep color and concentrated flavor.
Add the garlic and stir to combine.: During this stage you will see the mushrooms reduce in size and develop golden to deep brown spots, and a fragrant, savory steam will rise from the skillet. Stir occasionally to promote even cooking, scraping up any fond that forms on the pan because these browned bits add extra flavor. The why here is texture and concentration, because longer cooking removes excess water and intensifies taste. A typical pitfall is leaving them untouched too long and letting them stick, so stir gently if parts start to cling; a splash of heat adjustment helps if they are browning unevenly.
Taste the mushrooms and season with the desired amount of kosher salt and black pepper.: As you fold in the minced garlic , it will instantly release a bright, pungent aroma that rounds out the mushroom flavor. Keep the skillet over medium heat so the garlic becomes fragrant and melds with the other aromatics without turning bitter. The timing is deliberate because garlic browns faster than mushrooms and can scorch, introducing off flavors. If you notice the garlic darkening too quickly, reduce the heat and stir it into the moister parts of the pan to protect it while still developing its sweetness.
To serve, place one slice of toast on a plate, top with half the mushrooms, top with a fried egg, and sprinkle with Parmesan cheese.: This tasting moment is where the dish comes together, because you are balancing the earthy mushrooms and rich butter with the bright lift of Kosher salt and the warming bite of black pepper . Give a small taste and add salt in measured amounts, then re-taste, because mushrooms concentrate flavors while cooking. Over-salting is the most common misstep here; it is easier to add more later than to fix an overly salty pan. Adjust little by little until the seasoning feels lively but not aggressive.
To serve, place one slice of toast on a plate, top with half the mushrooms, top with a fried egg, and sprinkle with Parmesan cheese.: The final assembly is where the textures and flavors meet; you should notice the crisp, toasted sourdough holding up under the warm mushrooms while the fried egg adds a glossy, runny yolk that seeps into the bread. The grated Parmesan cheese melts slightly against the heat, adding savory depth and a gentle saltiness. Assemble on warm plates to keep everything comfortable, and avoid stacking too high which can make the toast soggy. A common serving mistake is letting the mushrooms cool too long before plating, which reduces their aromatics and the pleasure of the contrast between hot topping and crisp toast.