Preheat the Oven:

1. Preheat to 400°F (200°C) and line a large sheet pan with parchment paper or aluminum foil.

Prepare the Potatoes:

1. In a large bowl, toss the halved red potatoes with 1 tablespoon of olive oil, 1 tablespoon of sugar, salt, and pepper. Spread them out in an even layer on the sheet pan, turning the potatoes cut-side-down to get that golden brown crust.

Roast the Potatoes:

1. Place the pan in the oven and roast for 20 minutes.
Prepare the Sauerkraut: Drain and lightly rinse the sauerkraut with cool water. Squeeze dry and get as dry as possible. In a bowl, whisk 1 tablespoon of olive oil, 1 tablespoon of sugar, and Dijon mustard. Toss this with the squeezed-dry sauerkraut until well-coated.

Add the Bratwurst, Sauerkraut, and Onions:

1. Remove the pan, push the potatoes to the edges, sprinkle the sliced onions over the potatoes, and place the bratwurst and sauerkraut in the middle of the baking sheet.
Continue Roasting: Return to the oven for another 20 minutes, or until the bratwurst is golden and the potatoes have crispy edges.

Serve and Enjoy:

1. Garnish with fresh parsley, if desired, and serve hot with Dijon mustard or your favorite condiment.