I found this delicious version of a buttercream recipe in a book that I purchased from Amazon called Kauffeehaus by Rick Rodgers. This book is filled with delicious recipes of cakes, cookies, and donuts. I modified the recipe a little by adding 1/2 cup of icing sugar, which helped to thicken the consistency of the buttercream.
1 cup milk, divided
2 tablespoons cornstarch
2/3 cup granulated sugar
2 large egg yolks
1 cup (2 sticks) unsalted butter, at room temperature,
cut into small pieces
2 tablespoons Kirsch, or Cognac or golden rum
(can also use artificial liquor flavoring too
Pour 1/4 cup of the milk into a heavy bottomed medium saucepan, and add the cornstarch. Which to dissolve the cornstarch, then whisk in the sugar and yolks until smooth. Whisk in the remaining 3/4 cup of milk. Whisking constantly, being sure to reach into the corners of the saucepan, bring to a full boil over medium heat; the pastry cream will be thick. Remove from heat and transfer to a bowl set in a larger bowl of ice water. Stirring often, cool the pastry cream.
In a medium bowl, mix on high speed, beat the butter until smooth, about 1 minute. A tablespoon at a time, beat in the cooled pastry cream. Beat in the kirsch.