In a small sauce pot, melt butter and saute the onion until transparent, on medium heat.
Add whiskey and simmer for about 2-3 minutes.
Add beef stock, bay leaf and tomato paste. Using a silicone covered whisk, stir until all combined.
(To make the roux, combine 1/2 tbs soft (not melted) butter and 1/2 tbs of flour. Stir together very well.)
Whisk in the roux, salt and pepper. Simmer for about 5 minutes, whisking often. Take out the bay leaf before serving.
Burger:
Cook the burgers to your preference. I like to combine beef and pork ground meat and add some chopped onion, garlic clove, fresh herbs and a little bit of bread crumbs.
Saute mushrooms and onions until caramelized and add a little bit of whiskey sauce.
Top the burger off with sauteed mushrooms and onions, bacon and whiskey sauce.