Preheat oven to 350 degrees and grease a 13×9 baking dish. In a bowl, mix white cake mix, vegetable oil, water, and eggs together. Once combined, add in pumpkin puree, brown sugar, pumpkin pie spice, cinnamon, allspice and vanilla extract.
Beat brownie mix ingredients together by hand. Pour into a 9×13-inch greased pan. Bake at 350 degrees for 25-30 minutes. Cool good. While in pan cut brownies into small squares. Pour 1/4 c. Kahlua over brownies, let soak for 5 minutes. Mix 1 package pudding as directed, set aside. Mix another package pudding as directed, also set aside. LAYER IN A 9X13-INCH PAN: half of cut-up brownies, 1 of the pudding mixes, 1 carton Cool Whip, half of candy bars and half pecans. Repeat layers. Refrigerate for 2 hours or overnight.
Mix first 5 dry ingredients together. Add cream, put in round greased casserole dish. Mix additional cocoa, brown sugar and sugar together. Pour over ingredients in casserole. Pour 1 c. very hot water over all. Cover and bake at 350 degrees for 45-50 minutes. Serve with ice cream.