Classic Tunnel of Fudge Bundt Cake

Ingredients:

1 DEVILS FOOD CAKE MIX (PUDDING IN MIX KIND) IF NOT ADD 1/2 SMALL BOX OF INSTANT CHOCOLATE PUDDING (ONLY IF NOT ALREADY IN CAKE MIX)
EGGS, OIL, WATER
Chocolate Pudding Filling Recipe:
1/4 CUP COCOA 1 CUP GRANULATED SUGAR
1 CUP BOILING WATER (MICROWAVE)
3 TBSP. CORN STARCH 1 TSP. VANILLA 1 EGG