Cut the steak into small pieces, about 2cm x 1cm. Season well with salt and pepper.
In a frying pan, heat the butter over a high heat. Once it starts to foam add in the steak. Cook for around 6-8 minutes, moving occasionally and basting with the butter in the pan. Once the pieces are nicely caramelised, scoop them out of the pan and put on some kitchen paper.
Put the pan back onto the hob and reduce to a medium heat. Toss in the red onions and cook for about 8 minutes until they have softened. Don't overcook them, you still want to retain some of their moisture. Once cooked, take off the heat and leave to one side.
Lightly oil a muffin tray.
In a large bowl, mix together the eggs, sour cream and milk along with a good pinch of pepper, then slowly stir in the grated stilton.
Pop a tablespoon of the cooked red onion in each of the muffin moulds and then the pieces of steak. Make sure there is an even distribution of the ingredients. Then pour the egg mixture in to each mould, take care to get the same amount in each mould so that they cook evenly.
Pop the tray into the oven for around 30mins until the muffins are golden brown. Let them cool slightly before gently removing form the pan and serving.
While waiting for the muffins to cool, combine the ingredients for the horseradish dip to serve alongside.
Notes
Nutritional values are based on one of twelve muffins