We were chilling for the weekend, as one does when Sheltering in Place is the thing to do, and had a taste for burgers.
As it so happened, I had a pound of ground round and pork meatloaf mix in the fridge, and went through my files to see what looked interesting for a drizzly, cold spring day burger cooked on the stove.
I came across recipe for “Animal Style” In-N-Out burgers with mustard sauce, and thought, “why not?”
Ermmm… with a few, wee, tiny changes.
The resulting Mustard Onion is now one of my absolute favorite burger toppings; and it may very well be most excellent on most other sammiches as well.
First things first, let us talk about the mustard. I used home made honey mustard 
made with hot honey, yellow mustard, and Trader Joe’s (kinda zippy) Dijon mustard. If you cannot get to a Trader Joe’s, try using your fave Dijon and mebbe add a teaspoon or two of horseradish.
INGREDIENTS
Zippy & Sweet Mustard:
•1/2 cup Dijon mustard
•1/2 cup yellow mustard
•1/2 cup Mike’s Hot Honey
•1 tsp Aleppo pepper
Mustard Onion:
•2 tbsp unsalted butter
•2 tbsp Zippy & Sweet Mustard
•1 sweet onion, sliced
•1 tbsp Sherry Peppers Sauce*
*No Sherry Peppers Sauce? No Problem! Simply add a bit of decent sherry (none of that “cooking” stuff) and a dash or three of your fave hot sauce, to taste.
Make the mustard by combining the ingredients together until well blended. Transfer to a covered jar and store in the fridge until needed.
Note: I use this mustard blend a lot, and keep one of those condiment squeeze bottles of it in the fridge for ease of use and measuring out.
To make the mustard onion, melt the butter in a two quart saucepan over medium heat, then stir in the mustard.
Add the sliced onion and toss to coat well.
Reduce the heat to low and cook, stirring every now and then, for 90 minutes.
After about 45 minutes, I stirred in one tablespoon of Sherry Peppers Sauce and continued to cook.
After 90 minutes, the liquid was mostly cooked off, the onions were infused with all that flavor, and ready for the big time – slathered on top of a Swiss cheese burger on toasted artisan bread with a touch of mayonnaise and a pickle slice.
YUM.