Preheat the waffle maker. A mini waffle maker works best for chaffles, but a regular one is fine. Lightly grease the plates.
Make the batter. In a small bowl, whisk the egg.
Add almond flour, cocoa, granulated sweetener, baking powder, vanilla, and salt. Stir until mostly smooth. If using, fold in shredded mozzarella for extra structure.
Check thickness. The batter should be pourable but not runny.
If it’s too thick, add 1–2 teaspoons of water or almond milk. If too thin, sprinkle in a bit more almond flour.
Cook the first chaffle. Pour about half the batter onto the hot waffle iron. Close and cook for 3–4 minutes, or until set, crisp at the edges, and lifts easily.
Repeat. Cook the remaining batter.
Place cooked chaffles on a wire rack for 2 minutes to keep them crisp.
Make the filling. Stir Greek yogurt or softened cream cheese with powdered sweetener and a few drops of vanilla. Thin with a splash of almond milk if needed. Taste and adjust sweetness.
Assemble. Spread the filling over one chaffle and top with the second to create a sandwich.
For a lighter option, add filling only to half and enjoy open-faced.
Finish and serve. Dust with a pinch of cocoa or powdered sweetener, or drizzle with a little melted dark chocolate if you like.