How to Make It
Preheat oven to 325°F.
Weigh or lightly spoon flours into dry measuring cups; level with a knife. Combine flours, baking powder, and next 5 ingredients (through nutmeg) in a large bowl.
Place butter and sugars in a bowl; beat with a mixer at medium speed until light and fluffy (about 5 minutes). Beat in vanilla. Add eggs, 1 at a time, beating well after each addition. Combine yogurt and pumpkin in a bowl, stirring with a whisk. Add flour mixture and pumpkin mixture alternately to butter mixture, beginning and ending with flour mixture. Spoon batter into a 12-cup Bundt pan coated with baking spray. Bake at 325°F for 1 hour or until a wooden pick inserted in the center comes out clean. Cool in pan on a wire rack 30 minutes; remove cake from pan. Cool completely on wire rack.
Combine milk, corn syrup, and chocolate in a microwave-safe bowl; microwave at MEDIUM (50% power) 1 minute or until melted, stirring every 20 seconds. Slowly pour chocolate mixture over cooled cake.