Tartar Sauce. TARTAR SAUCE: Mix all of the ingredients together and refrigerate. MICROWAVE DIRECTIONS: Sprinkle the sole fillets with the salt and pepper. Fold in half and arrange in circle with folded sides to the outside edge in an ungreased microwavable pie plate, 9 X 1 1/4 inches. Mix the butter and lemon juice with the onion and drizzle over the fish. Cover tightly and microwave on high for 4 to 7 minutes, rotating the pie plate 1/2 turn after 2 minutes, or until the fish flakes easily with a fork.