Frito Pie

Bring vinegar, sugar, peppercorns, mustard seeds, and 2 teaspoons of the salt to a boil in a small nonreactive saucepan over medium-high. Boil, stirring often, until sugar and salt completely dissolve, about 5 minutes. Remove from heat; let cool 5 minutes. Place red onion slices in a pint-size glass jar. Pour cooled vinegar mixture through a fine mesh strainer into jar; press down on onion slices to ensure they are fully covered. Discard strained solids. Seal jar lid; let stand until onion slices are room temperature, about 15 minutes. Place in refrigerator for at least 30 minutes or up to 5 days. 

While onion slices cool, heat oil in small Dutch oven over medium. Add chopped yellow onion; cook, stirring occasionally, until translucent, about 3 minutes. Increase heat to medium-high, and stir in ground chuck; cook, breaking up meat with a wooden spoon, until browned, about 5 minutes. Add jalapeño, chili powder, cumin, garlic, black pepper, cayenne, and remaining 1 teaspoon salt; cook, stirring constantly, until fragrant, about 1 minute. 

Stir beer into mixture in Dutch oven; bring to a boil over medium-high. Boil, stirring often, until liquid slightly reduces, about 5 minutes. Reduce heat to medium-low, and add tomatoes with juices; cook, covered, stirring occasionally, 20 minutes. Uncover; cook, stirring occasionally, until reduced slightly and thickened, about 15 minutes. Remove from heat. Let cool slightly, about 10 minutes.

Lay chip bags flat on a work surface. Using a sharp knife or scissors, cut a vertical slit in center of each bag, leaving sealed edges intact. Spoon a heaping 1/3 cup chili over chips in each bag. Top with pickled red onion, shredded Cheddar, sour cream, and (if desired) jalapeño slices. Serve immediately.