First up, gather all of your ingredients.
Cook the pasta according to the directions and set aside. Pre heat the oven to 350 degrees.
Time to make the filling. In a pan, add in 1 tablespoon of butter and the chopped onion. Let it brown, about 4-6 minutes. Then add the peas. Cook for another 3-4 minutes. Put in a dish and set aside with the pasta.
Now, for the cheese sauce. In the same pan, melt the other 2 tablespoons of butter. Add in the flour and continually whisk until it's nutty and brown.
Pour in the milk and keep whisking. Add in the gouda cheese and the block of Boursin cheese. Again, keep whisking.
Once all of the cheese is nice and melty, add in the pasta, onion and pea mixture.
Stir all of the ingredients together. Pour into a 9x13 baking pan and bake at 350 for 20 minutes, uncovered.
Done! Looks so good.