Make the sriracha mayo - mix the mayo and sriracha in a small bowl.
Make the onions. Heat a non-stick pan over medium high heat, and melt the butter. Slice your onion as thin as you can manage and add to the pan. Reduce heat to low. Stir regularly until the onion is soft, mushy and golden brown - around 45 minutes.
Split and toast your brioche buns and spread a healthy dollop of the mayo on each half.
Crack eggs into a pan with a very large knob of butter. Cook them to your liking or according to the Ramsay method outlined above. Once nearly done, add the chopped chives and season with salt.
Pile the scrambled eggs on top of the buttom half of the brioche buns. Add a slice of american cheese on top of the eggs, then top the cheese with the caramelised onions. Top with the top half of the bun and enjoy.