Melt 3/4 cup unsalted butter in a light-colored saucepan over medium heat, swirling often, until it foams, then turns golden brown and smells nutty, about 5-6 minutes. Pour into a large heatproof bowl and let cool 10 minutes.

Whisk 3/4 cup brown sugar, packed and 1/2 cup granulated sugar into the browned butter until smooth and glossy.

Whisk in 1 large egg, 1 egg yolk, and 2 tsp vanilla extract until the mixture lightens slightly and looks well combined.

Let the dough rest at room temperature for 20-30 minutes — this helps the sugar dissolve slightly, which is key to the crinkled top.

Preheat oven to 350°F and line baking sheets with parchment. Scoop dough into 1.5 tbsp balls, spaced 3 inches apart (they spread).

Bake for 10-12 minutes, until edges are deeply golden and the centers still look slightly underdone and puffed. Firmly tap the baking sheet on the counter 2-3 times right when it comes out of the oven — this deflates the centers and creates the crinkled ripple texture.

Sprinkle immediately with 1/2 tsp flaky sea salt, for topping. Let cool on the pan for 10 minutes — they're very soft and thin right out of the oven — before transferring to a rack.