If starting with raw bacon: Cook bacon in large skillet until crisp. Remove bacon from pan, along with all but 2 - 4 tbsp of bacon grease.
If starting with cooked bacon: Melt butter over medium heat.
Add onion and cook until dark golden brown, stirring frequently and being careful not to scorch.
Meanwhile, cook pasta according to the package directions, reserving some of the cooking liquid.
Add half 'n' half and seasonings to onions in skillet. Add bacon back in. Heat to scalding. Turn off heat and add cheese, stirring until melted.
Add cooked pasta to skillet, using reserved cooking water to thin sauce as needed.
Option 1: Pasta is now ready to eat, or, if you used an oven-proof skillet, you can top it with crumbs and place under the broiler to brown for a few minutes. Watch it very carefully -- it will probably only take 3 - 4 minutes, and it goes from no color to burnt faster than small-town gossip.
Option 2: Pour pasta into buttered casserole dish (9"x13" or equivalent), top with crumbs and broil as above, OR cover with foil and refrigerate until later. When ready to bake, heat oven to 375F and bake, covered, for 40 minutes or until it gets bubbly. Remove cover and broil top briefly as above.