Melt the butter in a light-colored saucepan over medium heat. Stir until the milk solids turn golden and smell nutty- now you have browned butter. Remove from heat and cool 10 minutes.
In a large bowl, whisk the brown butter, dark brown sugar, and molasses until glossy and smooth.
Whisk in the egg, egg yolk, and vanilla.
Add flour, spices, baking soda, and salt. Use a spatula to fold until a soft dough forms.
Cover and refrigerate 45–60 minutes, or until scoopable and slightly firm.
Scoop 1-tablespoon balls, roll in the sugar mixture, and place on a lined baking sheet.
Bake at 350°F (177°C) for 8-9 minutes, or until the edges are set and the centers look slightly underbaked.
Let cool on the pan 5 minutes.
