Saute pork in butter for 4 minutes per side. Remove and keep warm. Add shallots and garlic. Saute until golden. Add vinegar and reduce by half. Add sorrel and half and half. Reduce by half. Add stock and allow to reduce for 5 minutes. Strain the sauce and swirl in the butter. Season with salt and pepper. Place pork on plates and pour sauce over them. Garnish with sorrel.