Preheat oven to 375 degrees. Shred all cheeses and butter a casserole dish for baking.
Boil pasta shells until al - dente, drain and rinse with cold water.
Cut bread into small 2” pieces and melt 1 tbsp butter over low heat. Mix butter and bread pieces, set aside.
Warm milk over low heat.
In high sided skillet, melt remaining 3 tbsp butter on medium heat. When butter bubbles, add flour.
Pour hot milk slowly into skillet, whisking constantly.
Stir in beer, salt, nutmeg, cayenne pepper, and black pepper. Add all but a small amount of shredded cheese and mix until melted.
Mix pasta and cheese sauce in casserole dish then add sliced bread pieces on top and sprinkle with remaining cheese.
Bake for 30 min, then broil for 2 min to slightly char bread. Let cool for 5 min and serve!