Heat a cast-iron skillet over medium-high heat and fry bacon until almost done, but not quite. Remove the bacon and drain on paper towel. Remove all but about 2–3 tablespoons bacon grease.

Toss Brussels sprouts with balsamic vinegar. Over a medium-high flame in the cast-iron pan, sauté the sprouts, cut side down, for about 6 minutes.

Turn on your broiler. Remove the cast-iron skillet from the flame. Cut up or break the bacon into pieces. Add bacon and almond slivers to the pan and toss everything together. Place under the broiler until almonds are toasted. Sprinkle liberally with shaved Parmesan.