Step 1

Combine flour and German lager beer in a medium bowl and whisk until smooth. Let stand at room temperature while preparing jalapeños.

Step 2

Bring a large pot of water to a boil. Cut a lengthwise slit down one side of each jalapeño, starting just below stem. Place jalapeños in the water, and return to a boil. Reduce heat and simmer 8 minutes or until jalapeños are just tender and not too soft. (Do not overcook. If chilies are too soft, they will be difficult to stuff without tearing.) Drain and refresh under cold running water. Wearing rubber gloves, carefully scrape out the seeds and membrane inside jalapeños using a small spoon or a melon baller. For hotter poppers, leave in some of the seeds.

Step 3

Drain sauerkraut and squeeze out excess liquid. Place sauerkraut on several thicknesses of paper towels, top with additional paper towels and press to squeeze out liquid. Combine sauerkraut and Tilsiter or Emmentaler in a small bowl and stir to mix well. Carefully fill each jalapeño cavity with about 3 tablespoons of the sauerkraut mixture. (The edges of the peppers do not have to seal.)

Step 4

Heat the oil for deep-frying in a large heavy deep-sided skillet or pot to 375 degrees F. Place the cornstarch in a shallow dish and, working with a few jalapeños at a time, dredge in cornstarch. Dip each jalapeño in beer mixture to coat completely. Fry jalapeños in batches, about 3 minutes, or until lightly browned. Transfer to a paper towel-lined plate to drain. Sprinkle peppers with the salt. Serve with mustard dip.

Step 5

Combine sour cream and mustard in a small bowl and stir to mix well.