Divide the cheese between 12 muffin cups. Trim and slice the spring onions (scallions) and add to the cups with the cheese.
Break the eggs into a jug and add the milk and pepper. Use a whisk or hand-blender to combine thoroughly. Continue to whizz for a minute or two until frothy.
Divide the egg mixture between the muffin cups - they should be just over ¾ full.
Bake at 190°C (375°F) for 10-15 minutes until risen, golden, and set in the middle. Remove from the oven and run a knife around the edge of each omelette muffin to loosen. Slip out onto a plate and serve warm.