Cake Layer: In a large bowl use a whisk to sift together the White Lily self-rising flour, granulated sugar, and cocoa powder.
Mix-in the half and half, oil and vanilla. Whisk until smooth.
Stir in 1/2 cup nuts and 1/2 cup chocolate chips until evenly distributed. The batter will be thick.
Spray the inside of a 6-quart oval slow cooker liberally with cooking spray. Spoon the batter evenly into the slow cooker.
Pudding Layer: Dissolve the espresso in the hot water to dissolve, then into the hot water mixture add the cocoa powder and brown sugar stirring until dissolved. Gently pour over the batter. Don't stir.
Place doubled paper towels over the slow cooker opening and place the lid on top. Cook on high for 2 hours. (Paper towels prevent condensation from dripping onto the cake)
Uncover and test the center of the cake portion with a toothpick. Remove the crock from the slow cooker. Allow to stand for 15 minutes.
The cake will appear cooked on top while the pudding forms on the bottom of the dish of the slow cooker. To serve, scoop into serving dishes and spoon the pudding over the cake.
Serve warm with a dollop of marshmallow cream, whipped cream or vanilla ice cream and a sprinkle of toasted nuts.