Add the onions and the vegetable oil to a large saucepan, over medium-low heat, and saute until soft. Stir in the black pepper, sea salt, vinegar, jalapenos, garlic and brown sugar until incorporated. Add half of the beer and let reduce until starting to get thick. Stir in the remaining beer and hot sauce and continue to reduce until the liquid is almost completely evaporated. Stir in the mustard and mix until combined.
Recipe by Kitchen Belleicious at https://kitchenbelleicious.com/2015/10/04/sweet-and-spicy-mustard-onion-relish/