French Buttercream Frosting Recipe

Name: French Buttercream Frosting Recipe
Ingredients: 5 1/2 ounces egg yolk (shy 2/3 cup; 155g), from about 10 large eggs; 5 1/4 ounces plain or lightly toasted sugar (about 3/4 cup; 145g); see note; 1 ounce bourbon, brandy, rum, tea, or coffee (about 2 tablespoons; 30g); 1/4 ounce vanilla extract (1 1/2 teaspoons; 7g); 1/2 teaspoon (2g) Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight; 16 ounces unsalted butter (4 sticks; 455g), softened to about 65°F (18°C)