Caraway seeds toast and infuse the butter as it browns, giving the Brussels sprouts a beautifully bronzed look and adding nutty depth.
Heat 1 1/2 teaspoons butter, oil, thyme, and caraway in a large nonstick skillet over medium-low, swirling until butter melts. Cook 2 to 3 minutes or until butter starts to foam.
Increase heat to medium-high. Add Brussels sprouts to pan; cook 6 to 7 minutes or until browned and crisp-tender. Remove from pan. Add onion and garlic to pan; sauté 6 minutes. Return Brussels sprouts to pan. Stir in syrup, vinegar, mustard, and salt; cook 2 minutes. Remove pan from heat; stir in remaining 1 tablespoon butter and pepper.