In pot of boiling, salted water, cook lemon slices, 30 seconds; drain; pat dry. Mix sour cream, heavy cream, 1 tsp. salt and 1/2 tsp. pepper. Stretch dough to fit oiled baking sheet. Spread with cream mixture; dot with ricotta. Top with lemon slices and thyme. Bake at 450 degrees until crust is golden, 15 minutes. Broil until lemons are brown in spots; season.