Soak cedar planks in water for at least 30 minutes.
Meanwhile, melt the butter in a large sauce pan over medium-high heat.
Stir in the sugar and let dissolve.
Add the onions, stir often, and caramelize, about 20 minutes. Do not rush them.
Add in the kraut, stir and let simmer 5-10 minutes.
Fire up your grill. Place the planks over the fire and let them get lightly charred on one side.
Flip planks and add the sausages and kraut.
Grill until the sausages are fully cooked, 15-20 minutes.
Lightly toast the buns, if desired. Top with the cooked sausages, kraut mixture, and a healthy serving of Sriracha mustard sauce. Add top bun and serve.