Creamy Eggless Chocolate Frosting

Ingredients

• 7 ounces plain or toasted sugar
• 2 ounces Dutch cocoa powder, such as Cacao Barry Extra Brute
• 1/4 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 32 ounces milk, any percentage will do
• 6 ounces heavy cream
• 12 ounces unsalted butter, softened to about 70°F

Directions

1. To make the base, put the sugar, Dutch cocoa, and salt into a 5-quart stainless steel or enameled Dutch oven, then whisk until the cocoa is evenly worked through the sugar. Pour in the milk and cream, whisking to combine. If a scale is handy, set the filled pot on it now and note the weight so you can monitor how much liquid cooks off. Set the pot over medium heat and cook, stirring now and then with a heatproof spatula, until the milk reaches a gentle simmer, about 12 minutes. If the timing is way off in either direction, nudge the heat up or down so the cooking pace lines up better with the next stage of the recipe.
2. Once the mixture is simmering, continue cooking while you stir and scrape the pot constantly, making sure milk solids do not collect on the sides or catch on the bottom. Cook until the base turns glossy, very dark, and pudding-thick, and has reduced to about 2 1/3 cups (24 ounces), about 30 minutes. Adjust the burner as needed if it is reducing too quickly or dragging along too slowly. If you weighed the pot at the start, it should now be 25 ounces lighter. Scrape the base into a shallow, wide container, such as a 7- by 11-inch baking dish, press plastic over it, and chill until it is cold and thick, or near 70 degrees F (21 degrees C), about 1 hour.
3. Scrape the chilled cocoa base into the bowl of a stand mixer with the paddle attached, and beat it until smooth. Add the softened butter a few tablespoons at a time, mixing as you go. Once everything is fully blended, change to the whisk attachment and whip until the frosting is pale, creamy, and smooth. It works best at about 70 degrees F; much cooler and it can look greasy or curdled, much warmer and it can turn loose and soft. If needed, adjust the texture using the buttercream troubleshooting guide here.