Measure the Brown Sugar. Typically light brown sugar but if you are looking for a deeper, richer taste you can try dark brown sugar. One important trick, make sure you sift out all the tiny brown sugar stones before you add the brown sugar to the mixing bowl. They will clog a decorating tip and are unappetizing to eat. Lightly pack the brown sugar and add it to the mixing bowl.
Add the butter and the vanilla extract to brown sugar in the mixing bowl. The butter needs to be “slightly softened” which is somewhere between straight out of the refrigerator and room temperature.
Mix the butter, brown sugar, and vanilla together on medium speed until thoroughly combined (at least 2 minutes.) You really want the brown sugar to dissolve and meld with the butter to enhance the flavor of the frosting and get rid of any graininess in the frosting.
Use a spatula to scrape the butter mixture down from the sides of the bowl before moving on to the next step.
Measure 1 pound of powdered sugar. If you don’t have a food scale, the equivalent would be 4 cups.
Add the powdered sugar to the butter/brown sugar mixture in the mixing bowl.
Start your mixer (or electric beater) on the lowest setting and keep it on low until the butter and sugar are incorporated (about 30 seconds). Stop the mixer and scrape down the sides of the bowl and then increase the speed to medium-high and mix for another 30-45 seconds so the frosting gets light and fluffy.
If the frosting is dry, add 1 teaspoon of milk and mix again.
Taste your frosting! You are trying to determine if the consistency is correct or if it needs more milk or maybe a little more vanilla extract. If it tastes great, test the consistency. Too thick? Add some milk and mix again to check to see if it is now the right consistency. The amount of milk to use depends on the state of your frosting and sometimes the time of year (if it is a hot humid day, you might not need to add any milk.) A good rule of thumb is to add the milk a teaspoon at a time.
