Preheat oven to 220°C grill (broiler) function. Line a baking dish with baking paper.
Pour 1.7 litres of water into the Thermomix bowl and insert the simmering basket. Boil 12 min/Varoma/speed 4 or until water has reached Varoma temperature. You will be able to see if the light has reached the correct temperature. Add time if needed. (Depends on the water temp as it goes into your Thermomix.)
Carefully place room temperature eggs into the basket using a spoon. Cook 11 min/Varoma/speed 3. If your eggs are cold or a different size, alter time to suit. Lowering cold eggs into very hot water is a recipe for disaster. Don't do it!
Remove basket of eggs carefully, using the Thermomix spatula. Peel eggs while warm, under cold running water. Slice eggs in half and scoop out the yolks, set aside.
Place cheese and 1 spring onion into a dry Thermomix bowl. Chop 8 sec/speed 9. Add prosciutto, sour cream, mustard, pepper and the cooked yolks and combine 10 sec/speed 5.
Place egg whites on the baking tray and spoon filling on top. Sprinkle panko all over and drizzle with melted butter.
Place into the oven for 5-7 minutes or until browned.
Garnish with remaining spring onion.