01 -
In a small saucepan over medium heat, melt the butter. Add the sliced onions and cook, stirring often, until deeply golden and caramelized (about 10–12 minutes). Stir in the brown sugar and water, simmer for 2–3 minutes until slightly thickened. Strain the syrup through a fine-mesh sieve, pressing to extract as much liquid as possible. Discard the solids. Let syrup cool.
02 -
Prepare 2 shots of espresso or strong brewed coffee.
03 -
Steam or heat the milk until hot and frothy. In each mug, combine 1 shot espresso and 1–1.5 tbsp onion syrup. Pour in the steamed milk, stir gently to combine, and adjust sweetness as desired.
04 -
Fill a glass with ice. Add 1 shot espresso and 1–1.5 tbsp onion syrup. Top with cold milk, stir well, and serve immediately.