Grease the holes with butter, slide the muffin tray into the lower half of a cold oven. Preheat the oven to 220°C.
Mix the flour, cheese, olives and salt in a bowl. Pour in the eggs, milk and butter, mix for approx. 1 min. using the whisk on a hand mixer. Spoon the batter into the hot, greased holes.
Approx. 30 mins. in the lower half of the preheated oven. Remove from the oven, allow to cool slightly, scatter the feta on top.