To brown butter, melt it on the stovetop over medium heat, stirring frequently. The butter will foam as it begins to melt. Once the foam begins to disappear you'll notice the milk solids settling on the bottom of the pan and beginning to brown. As the butter browns you'll start to smell a nutty aroma. When the melted butter turns a light brown color quickly remove it from the heat and pour into a glass bowl. There's a fine line between deliciously nutty brown butter and burnt butter, so be careful. But it takes practice! Place in the refrigerator to solidify. I like browning the butter the night before making the cupcakes.