For the pretzels:
1 cup milk
1 package active dry yeast
3 Tbsp packed light brown sugar
2 1/4 cups all-purpose flour, plus more for kneading
10 tablespoons unsalted butter, plus more for greasing
1 tsp fine salt
1/3 cup baking soda
2 Tbsp coarse salt

For the sauce:
1/4 cup mayonnaise
1/4 cup Dijon mustard
3 Tbsp packed light brown sugar
1/2 tsp cider vinegar