Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, granulated sugar, baking powder, and salt in a large bowl; stir with a whisk. Combine milk, bourbon, oil, and vanilla in a bowl. Add to flour mixture, stirring just until moist. Stir in dates and nuts.
Spoon batter into an 8-inch square baking pan coated with cooking spray. Sprinkle brown sugar over batter. Pour boiling water over batter (do not stir). Bake at 350° for 30 minutes or until the cake springs back when touched lightly in the center (cake will not test clean when a wooden pick is inserted in the center). Cut into squares. Serve each square with about 2 tablespoons warm Vanilla Sauce.