Preheat oven to 350 degrees and grease an 8x8 cake pan. If cranberries are frozen, thaw or run under warm water until no longer icy, set them aside. For cake, cream 3 Tb. butter, 1 cup sugar until fluffy. Mix flour and baking powder together and add to creamed mixture alternating with milk. Fold cranberries into batter gently. Flatten batter into pan. Cook for 25 or 30 minutes or until cake tests done. For sauce, combine the 1/2 cup butter, 1 cup sugar, and whipping cream in a pan and cook over medium heat until sugar dissolves and sauce thickens slightly. Add vanilla and serve warm with hot cake.