Thinly slice onion or shallot and add to a pan with olive oil, salt and pepper. Cook stirring often for about 20 min or until onion has softened and browned. Remove from pan.

Remove sausage from casing and push into tortilla in a thin even layer. You dont want this to get too thick as you want it to cook all the way through

Add butter to same pan add sausage tortilla face down. Cook for about 5 min or until sausage is nicely brown and then flip and cook for about 5 min on medium / low heat.

Remove from pan and wipe pan clean. Melt butter in pan and whisk 2 eggs in a bowl. Pour into pan in an even layer. Add onions and cheddar to the center, then fold each of the sides. This will help the cheddar melt.

Add to the center of the tortilla and fold over. Slice in half and enjoy!