2 Tbsp olive oil
2 lbs Gills yellow onions, slivered
1 lb unsalted butter, room temperature
¼ cup whole grain mustard
1 Tbsp salt
1. In a heavy bottom pot heat olive oil.
2. Add slivered onions to warm oil. Cook over medium heat for 20 minutes or until onions are golden brown.
3. Remove onions from heat and let cool to room temperature.
4. Using a countertop mixer fitted with a the paddle attachment, whip butter and salt together until light and airy.
5. Add mustard and cooled onion to butter. Mix until incorporated.
6. Transfer onion butter to a piece of parchment paper. Roll butter in parchment to form a log shape.
7. Transfer butter log to the refrigerator until ready for use.
8. To use, slice a coin of the butter log, remove paper and place on top of warm steak.