In a stand mixer with the dough hook attachment, combine the instant yeast, water, beer, bread flour, olive oil and sea salt.
Knead the dough for 8-10 minutes, or until a soft dough ball is formed.
Cover the bowl and allow to rise for 2 hours.
In a 2 quart saucepan, melt the butter over medium heat.
Add the flour and whisk continuously for 3-4 minutes.
Slowly add the milkto the saucepan, whisking continuously.
Allow the roux to thicken, whisking to prevent burning, for about 5 minutes. Stir in the mustard to the saucepan and remove from the heat.
Preheat the oven to 425℉.
Once the dough has risen, punch down the dough, remove from the bowl, and form into a ball.
Stretch the dough to a large 12-14 inch circle. Flour the bottom of the pizza pan and place the pizza dough on to the pan.
Spread the sauce over the dough, leaving 1 inch unsauced around the edges.
Using a pastry brush, brush the butter onto the outside crust.
Sprinkle one cup of cheese over the sauce.
Place the brat slices over the entire pizza, along with the sauerkraut.
Add the remaining cheese.
Bake in the preheated oven for 20 minutes, or until the bottom crust is brown and the cheese is hot and bubbly on top.
Remove the pizza from the oven to a cooling rack and allow to cool for 10 minutes before slicing.
While the pizza is cooling, sprinkle the diced yellow onion and diced pickles on top of the pizza.