IMBC from Whimsical Bakehouse Cake Book (Yield: 8 cups)
In a saucepan, bring to a boil:
1/2 cup water
2 1/4 cups sugar
Use a clean brush and cold water to wash down any sugar crystals that form on the sides of the pan as the water heats. When the sugar comes to a boil set a timer for 7 minutes, and let boil.
After 5 minutes, in the bowl of an electric mixer, begin to whip at high speed:
1 cup egg whites (about 12 large egg whites)
Whip until stiff. They should be done when the timer goes off.
With the mixer on high speed, slowly beat the sugar syrup into the egg whites, pouring the syrup to the side of the bowl to avoid the whip.
Continue to beat until the bowl is cool to the touch, about 10 minutes. Slowly add:
1 1/2 pounds (6 sticks) unsalted butter at room temperature, cut into 1-inch pieces
When the buttercream begins to jump out of the bowl, reduce the speed to low.
Mix in at low speed:
1 teaspoon pure vanilla extract
Beat until light and fluffy. At some points the mixture might look curdled. Just keep beating, it will become smooth again.
Stir in 2 to 3 ounces of melted, body temp (100 degree) semisweet chocolate per 1 cup of frosting. Mix until smooth and completely blended. Make sure you scrape the sides to you don't get hardened flecks of chocolate
stir in 14 cup lemon curd per 2 cups of frosting, mix until smooth and completely blended
stir in 1/4 cup (or to taste and color) raspberry puree per 2 cups buttercream. mix until smooth and completely blended
stir in 1/4 cup (or to taste and color) chocolate hazelnut spread (Nutella) per 1 1/2 cups frosting. you know the drill.
In a bowl, dissolve 2 tablespoons instant espresso powder in 2 tablespoons of hot water. Whisk in 3 cups of buttercream. mix it up until smooth and blended.