Yield: 4 cups
Begin by preparing the caramel. Using a heavy bottom sauce pan, heat the sugar on high until it melts. Lower the heat and allow the syrup to color. Make sure not to agitate the sugar to prevent crystallization. Remove from heat once syrup is an amber color and aromatic. Add in the heavy cream and whisk. Be careful as the mixture will bubble vigorously. Let cool slightly and add in the butter, bourbon and salt. Continue to whisk until homogenized. Let cool to room temperature.
For the buttercream, cook sugar and water in a pot until it registers 245 degrees F on a thermometer. Do not agitate the sugar as it cooks to prevent unwanted crystallization. You can also brush the sides of the pot with water to prevent crystal growth along the walls.
While the sugar is cooking, begin whipping egg whites on low speed. Whip to soft peaks and add the boiling sugar in a slow steady stream. Once all the sugar is poured, whip on high until the meringue is three times its original volume. Continue whipping on medium until the meringue is at room temperature.
Slowly add the soft butter to the meringue while whipping at low or medium speed. Whip until smooth and emulsified. Add cooled caramel, to taste.