Place butter in a small saucepan over medium-high heat. Stir occasionally until butter is browned and fragrant, about 5 minutes. Remove from heat and cool slightly.

Place slightly-cooled browned butter in a stand mixer fitted with a paddle attachment and add sugar. Beat on medium speed until combined. Add egg, yolk, peanut butter, vanilla, and yogurt to mixer and mix on medium speed until smooth and creamy.

In a separate bowl, combine flour, baking soda, and salt. Add flour mixture to liquid mixture and mix until a dough forms.

Roll cookie dough into 1-in balls and then gently roll around in additional sugar. Place 1-in apart on a parchment paper-lined baking sheet. Using a fork, gently press a criss-cross in each ball, flattening them slightly.

Bake cookies at 350F 9 minutes or until edges just start to turn golden (middles will still seem very soft---this ok) Cool cookies on baking sheet 5 minutes, then transfer to a wire cooling rack to cool completely. Enjoy IMMEDIATELY!