When mixture is hot, transfer to a mixing bowl , let cook to room temp, and mix till is stiff peaks. Mixture will be shiny and white. Add butter in few pieces at a time, mix on low until all butter is incooperated, its ok if frosting looks, lumpy. Continue to mix, add extract, pinch of salt, and room temp browned butter, browned butter should be solid at room temp. If not place in freezer for a few minutes.