Pat chicken dry, then toss with cornstarch, salt, pepper, paprika, and Italian seasoning until evenly coated.
Heat olive oil and 2 tbsp butter in a large skillet over medium-high heat until hot and shimmering.
Sear chicken in two batches, 3–4 minutes per side, until browned and just cooked. Transfer to a plate.
Reduce heat to medium-low. Add remaining 2 tbsp butter and garlic; cook 30–45 seconds until fragrant.
Stir in broth and lemon juice, scraping up browned bits. Simmer 1 minute to slightly reduce.
Return chicken and any juices to the skillet; toss to coat and warm 1–2 minutes. Finish with parsley and red pepper flakes.