3. Combine Wet Ingredients
Place the half and half, butter, and brown sugar in a small saucepan over medium-low heat. Stirring constantly, heat the mixture until the butter just melts and the sugar dissolves, 5 to 6 minutes. The liquid should never begin to bubble; if it does, turn the heat down.
Immediately remove the mixture to a heatproof bowl and let cool, stirring occasionally, for about 10 minutes, or until the outside of the bowl is warm to the touch but not hot.