Bring a large pot of salted water to a boil and cook the pasta according to package directions until al dente. Drain the pasta, reserving about 1/4 cup of the pasta water.

While the pasta cooks, whisk the eggs in a small bowl and set aside. If using, finely chop the onion or shallot and mince the garlic.

In a medium pan or the empty pasta pot (less washing!), heat a drizzle of olive oil or a knob of butter over medium heat. If using, add the chopped onion/shallot and cook until softened, about 3-5 minutes. Add the minced garlic (if using) and cook for another 30 seconds until fragrant.

Reduce heat to low. Add the diced Brie cheese and sour cream to the pan, stirring until the Brie is mostly melted and you have a creamy sauce. This should only take a minute or two on low heat.

Remove the pan from the heat immediately. Quickly pour in the whisked eggs and stir vigorously to combine with the warm sauce. The residual heat will cook the eggs, creating a thicker, carbonara-like sauce consistency. Do NOT return to heat, or you'll get scrambled eggs!

Add the drained pasta to the sauce. Toss to coat everything evenly. If the sauce seems too thick, add a tablespoon or two of the reserved pasta water until it reaches your desired consistency. Season generously with salt and black pepper.

While the pasta is resting for a moment, quickly assemble your simple salad by tossing the torn lettuce and sliced cucumber together.

Serve the creamy Brie pasta hot alongside the fresh green salad.