In a pan on medium heat, melt a knob of butter, then add slivered onion.

Once onions start to turn translucent, crush in the garlic. Continue sauteing on low-medium heat until onion has a caramelised colour.

Remove onions and set aside, cover with tinfoil to keep warmth.

Add oil to the pan, and start to sear the steak.

Whilst steak is searing, combine melted butter and the seasonings.

Once steak has finished searing, baste with the seasoned butter.

Remove the steak and set aside to rest.

Cut the bread in half, then toast in the pan with the remaining butter.

Slice the brie, then assemble the sandwich - with pesto and aioli slathered on each bun half.