1. Preheat the oven to 350°F (175°C) and adjust the oven rack to the lower-middle position.

2. To make your shiny, single-use Twinkie molds, start with a piece of aluminum foil, preferably heavy-duty, that’s approximately 14 inches long. It should be just a little longer than it is wide. Fold the foil in half lengthwise, then fold it in half again to create a rectangle that’s about 6 inches long and 7 inches wide. Repeat to make a dozen rectangles.

3. Place 1 sheet of folded foil on your work surface, with the long side facing you. Place a standard-size plastic or glass spice jar on its side in the center of the foil, the jar’s long side also facing you. Bring the long sides of the foil up around the jar. The foil won’t reach all the way around, and that’s okay. Fold the foil in around both top and bottom ends of the spice jar, nice and tight. You’ll end up with a sort of trough situation. (Cookbook author Todd Wilbur has a video of the process here; if you’re impatient, fast forward to 1:10, where the action starts.) Repeat until you have 12 foil Twinkie molds. Spritz the molds with an obscenely generous amount of nonstick spray or use your fingertips to coat the molds with vegetable oil. Place the Twinkie molds on a baking sheet or in a roasting pan.

4. Whisk the flours, baking powder, and salt together in a bowl.

5. Heat the milk and butter in a small saucepan over low heat until the butter melts. Remove from the heat add the vanilla. Cover to keep warm.

6. Separate the eggs, placing the whites in the bowl of a standing mixer fitted with the whisk attachment (or, if using a hand mixer or whisk, a large mixing bowl) and reserving the yolks in another bowl. Beat the whites on high speed until foamy. Gradually add 6 tablespoons of the sugar and the cream of tartar and continue to beat until the whites reach soft, moist peaks.

7. Transfer the beaten egg whites to a large bowl and add the egg yolks to the standing mixer bowl—there’s no need to clean the bowl (or, if using a hand mixer or whisk, simply place the egg yolks in a separate large bowl). Beat the egg yolks with the remaining 6 tablespoons sugar on medium-high speed until the mixture is very thick and a pale lemon color, about 5 minutes. Add the beaten egg whites to the yolks, but do not mix.

8. Sprinkle the flour mixture over the egg whites and then mix everything on low speed for just 10 seconds (or, if using a hand mixer or whisk, until blended but not thoroughly combined). Remove the bowl from the mixer, make a well in one side of the batter, and pour the melted butter mixture into the bowl. Fold gently with a large rubber spatula until the batter shows no trace of flour and the whites and yolks are evenly mixed, about 8 strokes.

9. Immediately scrape the batter into the prepared molds, filling each with about 3/4 inch of batter. Bake until the cake tops are light brown and feel firm and spring back when touched, 13 to 15 minutes. Transfer the pan containing the molds to a wire rack and allow the cakes to cool in the molds.

10. Just before filling, remove each cake from the foil. Using the end of a chopstick, poke three holes in the bottom of each cake, just like in the bottom of real Twinkies. Wiggle the tip of the chopstick around quite a lot to make room for the filling. (Again, you can see this in action here, beginning at minute 3.)

11. Transfer the frosting to a pastry bag fit with a small tip (about 1/4 inch across). Pipe the frosting into the holes you created in the bottom of the cakes. As you fill each cake, hold it in your hand and press your palm gently around it so you can feel the cake expand, taking care not to overfill and crack the cake.

12. Unlike real Twinkies, these won’t last indefinitely. They’re best served still slightly warm.