Pat chicken cutlets dry and season both sides with salt and pepper. Dredge lightly in flour, shaking off excess. Set aside on a parchment-lined baking sheet.

Heat a stainless steel pan over medium heat for 3 minutes. Add olive oil. Once shimmering, add 1 tablespoon butter and sear chicken for about 3 minutes per side until golden. Work in batches. Transfer chicken to a plate and tent with foil.

If needed, add more olive oil to the pan, then sauté garlic until lightly golden. Add chicken stock, grape juice mixture, and lemon juice. Increase heat and bring to a boil, scraping up browned bits.

Turn on the broiler and position rack to the second highest level.

When sauce reduces by half, turn off heat. Return chicken to the pan. Top each piece with roasted red peppers and mozzarella. Spoon a little sauce over each cutlet.

Broil until mozzarella is melted and lightly browned, watching closely.

Remove chicken to a platter. Whisk cold butter into the sauce one cube at a time. Season with salt and pepper, stir in parsley, and pour sauce over chicken before serving.