Line the bottoms of two well-greased 9-in. round baking pans with parchment paper; grease paper. In a microwave, melt chocolate; stir until smooth. Cool slightly.
In a large bowl, cream butter and sugars until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in chocolate. In another bowl, whisk flour, baking powder, cinnamon, salt, allspice and cloves; add to creamed mixture alternately with milk, beating well after each addition.
Transfer batter to prepared pans. Bake in a preheated 350-degree oven for 30-35 minutes or until a toothpick inserted in center comes out clean. Cool in pans 10 minutes before removing to wire racks; remove paper. Cool completely.
In a small saucepan, combine brown sugar, cream and butter. Bring to a boil over medium heat, stirring occasionally. Cook and stir 3 minutes. Remove from heat; gradually beat in confectioners' sugar and vanilla.
Place one cake layer on a serving plate; immediately pour half of the hot frosting over the cake. Top with remaining cake layer. Pour remaining frosting over top of cake. If desired, top with caramel popcorn.