Preparation Steps

• In a medium saucepan, whisk together the sugar, flour, and salt. Slowly whisk in the cold milk until completely smooth with no lumps.
• Set the pan over medium heat and cook, whisking constantly, until the mixture thickens to a glossy pudding consistency and small bubbles pop at the surface, about 5 to 7 minutes.
• Remove from heat and scrape the mixture into a shallow bowl. Press plastic wrap directly onto the surface to prevent a skin. Let cool to room temperature; do not use while warm.
• In a stand mixer with the paddle or a hand mixer, beat the butter on medium-high until very light and fluffy, about 3 minutes.
• With the mixer on medium, add the cooled milk mixture a tablespoon at a time, allowing each addition to incorporate before adding the next. Scrape the bowl as needed.
• Beat in the lemon zest, lemon juice, and vanilla. If desired, add a couple drops of yellow food coloring for a pale lemon hue. Continue beating until the frosting is silky and holds soft peaks.
• Use immediately to frost cooled cakes or cupcakes. If the frosting looks loose, chill for 10 minutes and re-whip briefly.