Take your wonton wrappers out of the freezer to bring them to room temperature.
Now it's time to make the filling! You can use a jar of pumpkin or squash baby food for the filling, but roasted squash is a snap—just cut your squash in half, take out the seeds, and lay the cut-side down in a casserole dish. Add about a 1/4 inch of water and bake at 350 degrees for about 40 minutes, until soft. Scoop out the cooked squash and mash with a fork.
Place the squash in a bowl and mix in the mascarpone cheese and the egg yolk. Sprinkle in some Parmesan cheese, salt, and pepper, to taste.
Lay about 12 of the wonton wrappers on a lightly floured surface and put a teaspoon of your squash filling in each wrapper. Wet your fingertip and run it along the edge of each wrapper, then fold in half, "sticking" the two sides together. If you have square wonton wrappers, you will now have ravioli triangles, if you have round wrappers, you'll have semi-circles.
Heat a pot of salted water and once it boils, put your ravioli inside. Cook 3-4 minutes, until the ravioli floats to the top.
Toss with a little butter and sprinkle with parmesan cheese.