Cake Layers:  Preheat oven to 325°F. Generously grease two 9-inch round nonstick (gray, not black) cake pans. Line bottoms with parchment paper or wax paper, then grease again.
Prepare cake as directed. Divide batter evenly in pans; smooth tops with spatula.
Place pans 3 inches apart on middle rack of oven and bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean. Cool cakes in pans on wire rack for 15 minutes. Run sharp knife around edges to loosen cakes, then invert onto separate plates to cool completely before frosting.
Custard Filling:  In a medium, heavy saucepan whisk together the sugar, cornstarch, and salt. In a separate bowl, whisk together the milk and egg yolks until very smooth and then stir into the sugar mixture.  *When using Rice Milk, increase the cornstarch to 1 1/2 Tb.

Place the saucepan over medium-low heat and cook, whisking constantly, until mixture comes to a boil and thickens. Remove from heat, stir in butter and vanilla, and transfer to a bowl; cover with plastic wrap touching surface and chill at least 2 hours.
Chocolate Glaze:  In a medium bowl, whisk together powdered sugar, cocoa, and salt until well blended. Stir in melted butter and vanilla with a spatula until well blended. Stir in water, if needed, 1 tablespoon at a time, until glaze reaches spreading consistency. Use immediately.
To assemble Boston Cream Pie:  Place 1 cake layer on a serving plate, topside down, and spread with chilled custard filling. Top with the other cake layer, topside up. Spread Chocolate Glaze on top of cake, allowing a little to drizzle down the sides. Serve immediately. Refrigerate leftovers.  Makes 20 servings.