Cook whichever meat you've chosen until it is nice and crisp, then drain well. One could also generally remove most of the fat from them pan, though save the fond in the pan (crispy little bits) and set this aside as well.
Put water on the boil for the pasta.
In a seperate pan, gently saute the garlic in the oil. After a minute or so, add the mushrooms, salt and pepper to taste and the rosemary sprig. Add more oil if necessary.
This next step will vary from cook to cook, depending on how thick or thin of a sauce is preferred. As the mushrooms cook, deglaze the meat pan with a bit of the white wine and cook off the alcohol. Lower the heat- we don't want to burn the sauce! At this point, add about 1 1/2 cups of milk (generally nonfat or 2%) and, as the milk begins to bubble at the edges of the pan, add flour, whisking all the while until the desired thickness is reached. While this is happening, add the nutmeg and cayenne pepper. Piment d'Espelette is a great alternative to the latter.
The water should be boiling at this point, so throw in the pasta and a pinch of salt.
When the mushrooms have cooked about 3/4 of the way through, add the frozen peas, stir to separate, and cover the pan for about five minutes, shaking it every so often so nothing sticks. This should heat the peas through and pretty much finish the 'shrooms.
Uncover pan and turn the heat up, to cook off any excess water quicklike. Remove rosemary sprig.
Add the sauce and meat to the veggies and warm through. Taste and add more salt or pepper as necessary.
Combine with drained pasta, garnish with cheese, and eat!