In a bowl, whisk together the eggs, cocoa powder, sweetener, milk, and baking powder until smooth and lump-free.
Pour the mixture into two small ramekins or heatproof cups.
Place a piece of dark chocolate in the center of each one (don’t push it all the way down).
Cook in an air fryer at 160°C (340°F) for 5–7 minutes, until the edges are firm but the center remains soft.
Alternatively, you can microwave it for about 60–90 seconds, depending on your microwave’s power. The center should still look slightly gooey.
Carefully remove and let cool for 1–2 minutes before serving.