butter, cubed and softened
- Whisk together the flour, sugar and salt in a saucepan until combined. Add the milk and cook over medium heat until it barely simmers (bubbles around the edge of the pan), whisking constantly. It will thicken slightly.
- Pour mixture into the bowl of a stand mixer and mix on high until the outside of the bowl is cool to the touch (about 8-10 minutes).
- Reduce the speed to low and add the butter (and vanilla extract if you are using it). Once the butter is incorporated, turn the mixer up to medium-high speed and whip until the frosting is light and fluffy (about another 3-5 minutes), scraping down as needed.
- If you are tinting your frosting, add the coloring and continue to whip until the color is evenly distributed.
- Use immediately to frost a two-layer cake, or 24 cupcakes.