Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: see manufacturer). Oil the pop-over tray and preheat in the oven.
For the filling, drain the olives and cut into slices. Pluck the cheese into 12 pieces.
For the dough melt butter, let it cool down a little. Mix eggs, milk and 1⁄2 TL salt with a whisk briefly. Stir in butter.
Add the flour at once and stir in quickly until the dough is just lump-free. Then fill the dough into a container with a pouring spout (e.g. measuring cup).
Remove hot sheet from the oven. Immediately fill each tray to 1⁄3 with dough. Spread olives and cheese on top. Pour the rest of the dough on top. Bake immediately in the hot oven for about 15 minutes. Then reduce the temperature (electric cooker: 175 °C/circulating air: 150 °C/gas: see
manufacturer). Continue baking for 10-12 minutes. Serve warm.