Prep: Trim the chicken and pat it dry with paper towels, then cut into 1½-inch pieces using a sharp knife.
Season the chicken with salt and toss with cornstarch until evenly coated.
Heat the oil in a large skillet over medium-high heat, then cook the chicken in a single layer until golden on all sides and fully cooked; work in batches if needed and set the cooked chicken aside.
Lower the heat and add the butter to the skillet, stirring as it melts.
Add the finely minced garlic and cook for 1–2 minutes until fragrant and just softened, not browned.
Return the chicken to the skillet and toss until every piece is coated in the garlic butter.
Serve immediately with fresh herbs and red pepper flakes if using.