Bring cream to a simmer, stirring occasionally, in a small saucepan over medium heat. Keep warm, covered.
Meanwhile, pour 1/4 cup water into a medium saucepan, then add sugar. Stir slightly just to moisten. Cook over medium-high, without stirring, until sugar turns a deep reddish amber, 12 to 15 minutes. (It will cook faster toward the end, so watch carefully.) Remove from heat and immediately slide in butter.
Drizzle in warmed cream (mixture will bubble up), stirring. When bubbles subside, return pot to low heat and stir until sauce is smooth.
Strain into a bowl, then stir in salt and bourbon. Set in a larger bowl of ice and cold water to cool to a spreadable consistency.
MAKE AHEAD: Up to 2 weeks, chilled airtight.