Cook Bratwurst on the grill and keep warm in a low over (175 degrees)
Heat oil over med-hi heat in a medium sauce pot, until it reaches 375 degrees
Whisk together milk, flour, beer, salt, and eggs to form a smooth, thin batter. Place cheese curds, about 6 or 8 at a time, into the batter, stir to coat, and remove with wire strainer or slotted spoon. Shake the curds to remove excess batter. Deep fry the curds until golden brown, 1 or 2 minutes. Drain on paper towels and season with salt.
Cut the bratwurst in half lengthwise
On the bottom bun, add mustard, Bratwurst, pickles, sauerkraut, cheese curds, and top with the other half of muffin.