Mise en place (always)! Pre-heat oven to 350°. Grease a glass casserole dish.
Mix together flour, cayenne pepper, smoked paprika, pepper, and salt in a bowl. In a separate dish, stir together heavy cream and milk.
Cook macaroni according to package directions. Drain. While macaroni is cooking, start on sauce below.
Melt butter in a medium saucepan. Sprinkle flour mixture over melted butter and stir until smooth. Heat on medium-low for 2 minutes, slightly browning.
Add 1/4 cup of cream/milk mixture to saucepan. Stir in (mixture will thicken initially). Slowly add rest of cream/milk mixture, 1/4 cup at a time, stirring well after each addition. Keep it on low heat, not quite a simmer. Continue with low heat, stirring often, for approximately 5 minutes.
Remove sauce from heat. Add cheese by the handful, stirring well after each addition.
Mix cooked macaroni and finished cheese sauce. Spoon into greased glass casserole dish.
Melt last 2 Tbsp. butter. Stir in bread crumbs and Parmesan cheese. Sprinkle mixture over top of macaroni.
Bake in 350° oven for approximately 30 minutes or until bubbly and top begins to brown. (If top is browning too much, cover with foil and then continue baking.)
***For quick reference, 3/8 is equal to 1/4 plus 1/8.