Rub mustard onto the fillet and leave it for 20-30 minutes to marinate
Cook the fillet either on the griddle or bbq, then leave on the side
Add half the butter, olive oil and onions into a pot and slow cook to caramlize for 20 minutes
In a separate pot add the rest of the butter, crushed garlic and parsley for a few minutes on a low heat to combine
Put the sliced tomatoes onto a griddle pan and slow cook for about 8-10 minutes
In a small bowl add the mayonnaise and hot sauce and mix well together. Use a sriracha, bajan or even tabasco (whatever your preference is)
Spread the garlic butter mixture onto one side of the bread and put it in the oven
After a few minutes remove the bread and then put thinly cut slices of beef fillet, tomatoes, caramelised onions layered.
On the other remaining bread slather on the spicy mayonnaise
For the final touch, add a fried egg on the sandwich and enjoy!