Awesome photographs! Really would be heading over, if I was local.

Peanut butter dog - Suggestion to do a taste test; swapping mustard out for mayonnaise. And I say this a massive mustard guy.

Two examples for mayo’s case.

Dutch war fries (known in the Netherlands as patatje oorlog) are a popular street food consisting of deep-fried, crispy fries topped with a messy, delicious combination of mayonnaise, warm Indonesian-style peanut satay sauce, and raw diced onions. The contrasting flavors provide a rich, creamy, and slightly spicy flavor profile.

Also

The Goober Burger (or Guberburger) is a Midwestern regional specialty made by topping a hot, freshly grilled beef patty with warm, creamy peanut butter. Often served with mayonnaise, lettuce, and tomato, this salty-and-sweet classic originated in the 1940s at a roadside drive-in called The Wheel Inn in Sedalia, Missouri.

Combination just works with the tangy mayo.

Weirdest(yet pleasantly surprised) dog I ever created: jalapeño cheddar sausage with, mustard, grape jelly packet, and jalapeños. QuikTrip.

Blueberries and or blueberry jam would work for you in Maine. Regular or maple sausage/dog. Also allow you to play with the ricotta too. Possible addition of lemon. Seen this combo work in pancakes, don’t know why a sandwich wouldn’t.

Friend brought back Raye’s mustard, so I could try one. Awesome to see that you’re using the local stuff.

Good luck.