Teriyaki-Style Brussels Sprouts

Place a rack in middle of oven; preheat to 425°. Toss 2 lb. brussels sprouts, trimmed, halved, and ½ cup extra-virgin olive oil in a large bowl; sprinkle with 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt and season with freshly ground pepper. Spread out brussels sprouts in a single layer on a large rimmed baking sheet and roast, tossing halfway through, until deeply browned and tender, 30–40 minutes.

Meanwhile, bring 3 garlic cloves, smashed, ¼ cup soy sauce, 3 Tbsp. (packed) dark brown sugar, and ¼ cup water to a simmer in a small saucepan over medium heat. Cook, stirring occasionally with a wooden spoon, until sugar is dissolved and small bubbles form around the edges of pan, about 2 minutes. Reduce heat to medium-low and cook, stirring often, until sauce is slightly thickened, about 5 minutes.

Whisk 2 tsp. cornstarch and 1 Tbsp. water in a small bowl, then slowly whisk slurry into sauce. Cook, stirring, until sauce thickens further (spoon should leave a trail when dragged through), about 1 minute. Add 1 Tbsp. unsalted butter and stir until incorporated and sauce is syrupy. Remove from heat and stir in 1 Tbsp. apple cider vinegar; fish out garlic and discard.