Add butter to a small saucepan set over medium heat and cook, stirring constantly, until butter begins to lightly foam and turns from light yellow to golden brown, about 5 minutes. Turn off heat and set aside to cool.

Combine room temperature browned butter, brown sugar, and granulated sugar in a bowl and beat with an electric mixer until well combined. Add egg, egg yolk, and vanilla extract and mix until thoroughly combined.

In a separate bowl, combine flour, salt, and baking soda. Gradually add the flour mixture to the butter mixture, 1 tablespoon at a time, until well combined. Refrigerate for at least 1 hour or overnight until chilled.

Preheat the oven to 350 degrees F (175 degrees C) and line a sheet with parchment paper.

Measure out 1-inch portions of the batter with a spoon or use an ice cream scoop to cut out balls. Place dough balls on the prepared baking sheet roughly 2 inches apart.

Bake in the preheated oven until the edges begin to turn just golden brown, 11 to 12 minutes. Set aside to cool.

Prepare the chocolate shell during cooling. Add coconut oil to a small bowl and melt in the microwave for 30 seconds. Add chocolate chips and stir until chocolate has thoroughly melted. Set aside.