3/4 cup granulated sugar 1/3 cup all-purpose flour 1/4 teaspoon salt 3 cups whole milk 3 large egg yolks
3 large egg whites, at room temperature 1/4 teaspoon cream of tartar 6 tablespoons granulated sugar 1/2 teaspoon vanilla extract
In a medium saucepan, whisk together the sugar, flour, and salt. Gradually whisk in the milk until smooth.
Cook over medium heat, stirring constantly, until the mixture thickens and comes to a boil, about 10-12 minutes.
In a small bowl, lightly beat the egg yolks. Gradually whisk in about 1 cup of the hot milk mixture.
Pour the egg mixture back into the saucepan with the remaining milk mixture, stirring constantly.
Bring the mixture back to a gentle boil and cook for an additional 2 minutes, stirring constantly.
Remove the saucepan from the heat and stir in the butter and vanilla extract until the butter is melted and the mixture is smooth.