Wisconsin Butter Burgers

In a small bowl, use a fork to thoroughly blend the softened butter and soy sauce until thoroughly mixed with a uniform color and texture. On a sheet of plastic wrap, form the compound butter into a roughly 5-inch long log. Wrap tightly and freeze until firm, about 15 minutes or refrigerate until ready to use.

When ready to proceed to the next step, halve the log, then refrigerate one half and cut the remaining half into 1/4-inch dice.

On a parchment paper lined rimmed baking sheet, distribute sirloin cubes and 1/4-inch butter cubes in a single layer and freeze until the butter and beef cubes are firm, at least 30 minutes.

While beef and butter are chilling, slice off 1 tablespoon (14g) of the remaining compound butter. (If you don't have a kitchen scale, just eyeball it.) Refrigerate the remaining unused butter. In a medium saucepan, melt the portioned 1 tablespoon compound butter over medium heat. Once melted, add onion, 1 tablespoon water, and a generous pinch of salt. Stir to combine and cover and cook until onion is soft and translucent, 4 to 6 minutes. Uncover and continue to cook, stirring frequently, until onion is beginning to brown, 2 to 6 minutes. Remove from heat, stir in lemon juice; set aside.

For grinding the meat with a meat grinder or stand mixer with meat grinder attachment: Once beef and butter are chilled, grind them together in small batches to ensure that the mixture remains cold, and taking care to ensure a consistent balance of beef to butter in every batch. If not shaping burgers immediately, you can hold ground beef and butter in a covered bowl in the refrigerator for several hours.

For grinding the meat with a food processor: Working in 2 batches, in a food processor, pulse beef and butter, taking care to ensure a consistent balance of beef to butter in each batch, until finely ground into roughly 1/16-inch pieces, about 20 pulses, stopping to redistribute mixture needed; return to sheet. Discard any long strands of gristle. If not shaping burgers immediately, you can hold ground beef and butter in a covered bowl in the refrigerator for up to 24 hours.

When ready to cook, divide the ground beef mixture into four (about 4-ounces each) balls and shape into 4 1/2-inch-wide by 1/2-inch-thick patties. Transfer to a large plate, cover, and refrigerate for at least 15 minutes. Slice the remaining butter into 4 equal slices. If necessary, warm the sautéed onions in the microwave, about 30 seconds on high.

In a 12-inch cast-iron or stainless-steel skillet, heat 1 teaspoon oil over medium-high heat until just smoking. Season both sides of the patties generously with salt and pepper. Carefully transfer the burgers to the skillet and cook until well browned on both sides and cooked through (for medium rare, cook to 135℉), 2 to 3 minutes per side. Transfer cooked burgers to a plate, lower the heat to medium-low, and toast the buns in the skillet, face-down, in two batches if necessary.

To assemble the burgers, place one patty on the bottom half of a bun. Top with 1 slice of reserved compound butter and a generous spoonful of onion, followed by the top bun. Compress to encourage melting. Repeat. Serve immediately.