1 c. sifted cake flour
3/4 tsp. baking powder
1/8 tsp. salt
1/3 c. milk
3 tbsp. vegetable oil
3 lg. room temperature eggs
1 egg yolk
2/3 c. sugar
1 tsp. vanilla
1/2 recipe Boston cream filling - recipe followed
Powdered sugar
Chocolate sauce

Put rack in lower third of oven and heat to 350 degrees. Line a 9 inch springform pan with parchment or waxed paper; don't grease. Sift together flour, baking powder and salt. Combine the milk and oil in a small bowl; don't worry if they don't blend together. Whisk together the eggs, yolk and sugar in a large mixing bowl. Using an electric mixer at medium speed, beat the egg mixture until it is light ivory in color and very fluffy, about 6 minutes, adding the vanilla toward the end. Using a rubber spatula, fold in the flour mixture in 2 additions. Pour the milk mixture down the side of the mixing bowl (it will sink to the bottom of the bowl under the batter). Gently fold until it is thoroughly incorporated. Pour the batter into the pan. Bake 25 to 30 minutes, or until the cake is golden on top and it springs back when lightly pressed in the center. Remove pan from oven to a wire rack until cool. To assemble the dessert: Split the cake into 2 layers. Spread half the filling evenly over the bottom cake layer. Center the other layer on top. Place the cake on a serving plate, cover with plastic and refrigerate. Before serving, sprinkle top of cake with powdered sugar. Spoon warm chocolate sauce onto individual plates. Using a serrated knife, slice dessert into pie shaped wedges and center each portion on the sauce.