01 -
Melt 1 tablespoon unsalted butter in a large cast-iron skillet over medium heat. Once melted, add the sliced onions and sauté for 5 minutes until they begin to soften. Reduce heat to low, sprinkle with 1 teaspoon sugar, and stir frequently for 20–30 minutes, allowing the onions to develop a deep golden color and sweet aroma. If browning too quickly, decrease heat. Deglaze with 1 teaspoon balsamic vinegar and 1/4 teaspoon salt, stirring until the liquid is absorbed. Remove from heat and cool to room temperature.
02 -
Preheat oven to 425°F. Line a baking sheet with parchment paper. In a large bowl, whisk together all-purpose flour, 1 tablespoon granulated sugar, baking powder, garlic powder, dried parsley, and kosher salt. Cut in 8 tablespoons cold salted butter using a pastry blender or fingertips, working until the mixture resembles coarse crumbs.
03 -
Stir in the cooled caramelized onions and shredded Gruyere cheese until evenly distributed. Pour in 3/4 cup whole milk and gently mix, adding up to 1/4 cup more milk only as needed, until just combined. Do not overmix; a slightly shaggy dough is ideal.
04 -
Using a spoon or medium scoop, drop 2-tablespoon portions of dough onto the prepared baking sheet, spacing apart. Bake for 10–12 minutes, or until biscuits are golden brown on the outside and lightly springy to the touch.
05 -
Melt the remaining 2 tablespoons salted butter in a small microwave-safe bowl (approximately 20 seconds). Stir in a pinch of dried parsley if desired. Brush the freshly baked biscuits with the melted butter and serve warm.