IN A LARGE RESEALABLE PLASTIC BAG, ADD FLOUR, SALT AND PEPPER. SEAL AND SHAKE. SHAKE A FEW PIECES OF CHICKEN IN BAG AT A TIME TO COAT WITH FLOUR MIXTURE; SET ASIDE. REPEAT WITH REMAINING BREASTS.
IN A LARGE SKILLET OVER MEDIUM, MELT BUTTER. ADD CHICKEN AND SEAR SKIN-SIDE-DOWN, COOKING ABOUT 4 MINUTES UNTIL SKIN IS GOLDEN BROWN. PLACE CHICKEN SKIN-SIDE-UP IN SLOW COOKER CROCK.
POUR WINE, LEMON JUICE, BROTH AND CAPERS OVER CHICKEN.
COVER AND COOK ON HIGH FOR 2 HOURS OR LOW FOR 4 HOURS UNTIL CHICKEN IS COOKED THROUGH AND TENDER.
REMOVE CHICKEN TO A SERVING PLATTER. COVER WITH FOIL AND KEEP WARM.
IN A SMALL BOWL, STIR WATER AND CORNSTARCH UNTIL CORNSTARCH IS DISSOLVED.
TRANSFER LIQUID FROM CROCK TO A MEDIUM SKILLET. STIR IN CORNSTARCH MIXTURE.
PLACE SKILLET OVER MEDIUM-HEAT. COOK ABOUT 3 MINUTES, STIRRING CONSTANTLY UNTIL MIXTURE IS SLIGHTLY THICKENED.
POUR MIXTURE OVER CHICKEN. GARNISH WITH LEMON SLICES.