Chicken:2 pounds skin-on chicken3/4 cup cornstarch, plus more if needed1 tablespoon baking powderSauce:4 tablespoons olive oil2 tablespoons butter, plus more if needed5 cloves garlic, grated1 teaspoon smoked paprika1/2 teaspoon crushed red pepper, more or less to taste1/4 teaspoon cumin2 tablespoons lemon, plus moreSalt and pepper