Preheat oven to 350 degrees F (175 degrees C). Bring a saucepan of water to a boil. Add potato and cook until tender but still firm, about 15 minutes. Drain, cool and mash. Grease and flour a 10 inch Bundt pan.
Cream butter, gradually add brown sugar until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in mashed potatoes.
Combine flour, baking powder, cinnamon, nutmeg, and cloves; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Stir in melted chocolate and pecans. Pour batter into a prepared 10 inch Bundt pan.
Bake at 350 degrees F (175 degrees C) for 1 hour or until cake tests done. Cool in pan 20 minutes; remove cake from pan, and cool completely before serving.