Beat butter and brown sugar at medium speed with an electric mixer until blended; add eggs, beating well. Stir in melted chocolate, 1 teaspoon vanilla, and next 3 ingredients. Pour into Chocolate Tart Shell.
Bake at 375° for 20 minutes. Cool on a wire rack 30 minutes.
Beat cream at high speed until foamy; gradually add granulated sugar, beating until soft peaks form. Stir in remaining 1 teaspoon vanilla. Dollop cream around tart; garnish, if desired.
Chocolate Tart Shell: Combine 1 1/4 cups chocolate graham cracker crumbs and 1/3 cup melted butter; press into the bottom of a 10-inch tart pan. Bake at 350° for 6 minutes; cool on a wire rack.