Bratwurst Potato Bake

2 lbs potatoes, any variety, scrubbed, cut into 3/4 inch chunks
1 large onion, diced large
1 package fresh bratwurst (4 bratwurst), cut into bite size pieces
2-3 tablespoons fat of your choice: melted bacon grease, olive oil, melted clarified butter
4 tablespoons grainy mustard, divided
sea salt and black pepper

1. Heat oven to 425°F. Toss the potatoes and onion with the fat and 3 tablespoons mustard in a bowl. Add a generous sprinkling of salt and pepper. Spread potatoes and onion on a rimmed baking sheet and bake for 30 minutes.
2. Toss the bratwurst in the remaining tablespoon of mustard until coated. Remove potatoes from the oven and spread the bratwurst among the potatoes. Return pan to oven and bake another 20 minutes or until the potatoes are browned and tender.