Salted Brown-Butter Latte

Steps

1. Make the brown-butter syrup: Cut the butter into pieces and melt in a 2-quart saucepan over medium heat. Cook, swirling the pan often, until the butter foams, then the foam subsides and the milk solids turn deep amber with a nutty, toffee-like aroma, 4–6 minutes. Watch closely — it goes from amber to burnt in seconds, so pull the pan off the heat the moment it smells nutty and the solids are golden-brown.
2. Immediately whisk in the brown sugar and water — the mixture will bubble and seize briefly, then loosen. Return to medium-low heat and simmer, whisking, until the sugar is fully dissolved and the syrup is glossy and slightly thickened, 2–3 minutes. Remove from the heat and stir in the vanilla and the ¼ teaspoon flaky salt. Simmering the sugar-and-water base is what keeps the browned butter emulsified: it suspends the butterfat and browned milk solids so the syrup won't separate into an oily slick when it hits hot milk.
3. Cool the syrup slightly, then pour into a small jar. You'll use 2 tablespoons per latte; the rest keeps for up to 2 weeks in the refrigerator.
4. Build the latte: Pull 2 shots of espresso (about 2 ounces) into a warmed mug, or brew 4–6 ounces of strong coffee.
5. Steam the milk: Heat the milk in a 1-quart saucepan over medium heat until just steaming and small bubbles appear at the edges, about 150°F — do not let it boil. Whisk or froth until foamy.
6. Add 2 tablespoons of the brown-butter syrup to the espresso and stir to dissolve. Pour in the steamed milk, spooning a little foam on top.
7. Finish with a pinch of flaky sea salt over the foam and serve immediately.