Pound chicken breasts between layers of heavy plastic wrap until even thickness, about 1/2" thick.
Stir salt and pepper into flour. Dip both sides of chicken into flour, shaking off excess. (Discard any remaining flour.).
Melt butter in a large skillet over medium-high heat. When foaming subsides, reduce to medium and add chicken. Cook until browned on both sides, 4-6 minutes per side. Transfer to plate and cover loosely with foil.
Add garlic to butter and saute until fragrant, about 1 minute.
Add wine and scrape up any browned bits from bottom of pan. Simmer 3-4 minutes. Add dill, lemon zest, lemon juice, cream and capers. Simmer until slightly thickened. Adjust salt and pepper in sauce if needed. Spoon over chicken and serve with rice or couscous.