Heat butter in a pan over high heat until frothing.
Pour in egg mix. Turn down heat slightly. Gently push cooked egg to the middle of pan with a wooden fork, allowing uncooked egg to run underneath.
When omelette is set on top - and browned underneath, spread with Maille® Old Style mustard, sour cream and sprinkle with chopped ham. Flip omelette over and slide onto a serving plate.
Best served with tomato salad, tossed in vinaigrette with basil leaves.