Preheat your oven to 350°F (175°C). Line a 12×16-inch baking sheet with parchment paper and lightly grease it so the sponge releases easily later. Set it aside.

Separate the eggs, placing the egg whites in a large mixing bowl and the yolks in a smaller bowl. Add the cream of tartar to the whites and whip on medium-high speed until they form stiff, glossy peaks. The foam should hold its shape when you lift the beater.

In the bowl with the egg yolks, whisk together the yolks, powdered sweetener, and vanilla until the mixture becomes pale, slightly thick, and smooth. This step helps build structure and sweetness into the sponge.

Add the almond flour, coconut flour, and salt to the yolk mixture. Whisk or fold gently until the dry ingredients are fully incorporated and no lumps remain. The batter will be thick at this stage, which is normal.

Add a small scoop of the whipped egg whites into the yolk batter and fold gently to lighten it. Then add the remaining whipped whites in two or three additions, folding slowly and carefully to avoid deflating the air you just whipped in. Stop folding as soon as no streaks remain.

Pour the batter onto the prepared baking sheet and spread it out evenly with a spatula. Aim for a smooth surface and an even thickness so the sponge bakes uniformly. Bake for 10–12 minutes, or until the top feels springy and the edges are lightly golden.

Let the sponge cool for about a minute, then flip it carefully onto a sheet of clean parchment. Peel off the baking parchment from the bottom. Allow it to cool just slightly, then use a serrated knife to cut the sponge into 12 equal rectangles. Handle them gently to prevent tearing.

Beat the softened cream cheese and butter together until smooth and fluffy. In a small saucepan, melt the allulose with a splash of water and espresso until it turns slightly golden and caramel-like. Let it cool slightly, then fold it into the cream cheese mixture until the filling becomes silky and pipeable.

Transfer the filling into a piping bag. Insert the tip into the underside or side of each sponge rectangle and gently squeeze to fill each Twinkie with the caramel-coffee cream. Add just enough filling so the Twinkie feels full but not bursting.

If using the optional caramel glaze, whisk melted butter, cream, and allulose together until smooth. Brush a light layer over the tops of the Twinkies for shine. Place the filled Twinkies in the fridge for 20 minutes to set the filling and improve the texture before serving.