- 1/2 pound (2 sticks) unsalted butter, melted
- 2/3 cup heavy cream
- 2/3 cup unsweetened coconut milk
- 1 cup granulated sugar
- 1/3 cup packed light brown sugar
- 1 large egg yolk, beaten
- 1 cup dark rum
- Combine all the ingredients except the rum in a small saucepan and cook over medium-low heat, whisking constantly, until the sauce has thickened and coats the back of a spoon, about 10 minutes. Do not allow the sauce to boil or the egg will curdle and the sauce will not be smooth. (If this does happen, then simply strain through a fine-mesh sieve.) Remove from the heat, stir in the rum, and set aside to cool slightly.