Preheat oven to 400°F. Pat 2 lbs boneless skinless chicken thighs dry with paper towels and season both sides with salt and black pepper. Sprinkle 2 tsp of the cornstarch evenly over the chicken and rub lightly to coat.

In a bowl, whisk together ½ cup lemon juice, ¾ cup brown sugar, ½ cup tomato sauce, 1 Tbsp soy sauce, and 1 tsp garlic powder until smooth. In a separate small bowl, stir 1 tsp cornstarch with 1 Tbsp water to make a slurry, then whisk it into the sauce mixture.

Heat 1 Tbsp butter in an oven-safe skillet over medium-high heat. Add the chicken thighs and sear for 4–5 minutes per side until golden brown. Transfer the chicken to a plate.

Reduce heat to low and add the prepared sauce to the skillet. Stir and warm gently for 1–2 minutes until slightly thickened.

Return the chicken to the skillet and spoon sauce over the top. Transfer the skillet to the oven and bake for 20–25 minutes, flipping halfway through, until the chicken reaches 165°F and the sauce becomes thick and caramelized.