Step 1

In a medium saucepan over high heat, melt the butter. Continue cooking, stirring occasionally, just until the butter turns a pale golden brown, about 2 minutes. Stir in the pecans, and decrease the heat to medium-high. Stir in the brown sugar, cooking and stirring it until it melts and you no longer see sugar crystals in the pot, about 4 minutes. Carefully stir in the heavy cream, starting with about a third of it before adding the rest: The mixture will bubble up, so stir gently and constantly so that it does not boil over. Continue cooking until the brown sugar fully dissolves into the cream, about 2 minutes. Remove from the heat.

Step 2

Stir in the whisky (if using), vanilla and salt. Let cool on the counter for at least 30 minutes, and up to overnight, before serving.