I use mustard as a binder on brisket and pork shoulders and I am still confused on how it just goes away completely during the cook.
For scientific research I had a Culver’s butter burger last night. I still like Whataburger more and found the butter burger more salty and fat tasting it lacked that sharpness from mustard and jalepenos in a Whataburger. The one part I liked of the butter burger was that the edges had a nice crisp char that was good whereas the Whataburger texture was softer.
I guess it's a similar take like butter on steak while grilling. Grill them buns with butter and hamburger grease and your heart will love you for killing it.
No idea if they're still there ("limited time"), but their jalapeno/cheddar biscuits are so freaking good, infinitely better than their regular ones. Also, basic Frenchy's-style yellow mustard is nasty on everything. Real mustard is awesome. Bought some hotdogs for the first time in a long time (Boar's Head uncured beef, because I am a fancy boy), HEB brioche buns. We had some with sauerkraut, whole grain mustard and swiss; and some with grilled onions/peppers, a bit of cholula+ketchup, and cheddar. So damn good, dangerously good in fact.
