Heat a heavy-bottomed saucepan over medium heat and sprinkle in the sugar. Watch it like a hawk; sugar can go from golden to burnt faster than you can say “crystal.”
Stir constantly with a heatproof spatula until the sugar melts into a thick amber liquid. No clumps, no hiding bites of sugar—keep it smooth. If you see lumps, lower the heat and keep stirring.
Remove from heat and whisk in the butter until fully melted and incorporated. The mixture will bubble up—that’s normal. Stay calm, this is where the magic happens.
Slowly whisk in the cream while the pan sits off the heat. It might hiss, it might foam, it might giggle at you—just keep whisking until it’s silky and smooth.
Return to low heat for a minute or two if you want it extra glossy. Stir in salt and vanilla if using. Let it cool a few minutes before pouring into a jar. It thickens as it cools, so don’t panic if it seems loose.
Transfer to a heat-safe jar or bottle. Let it chill in the fridge, then give it a sniff when you open it—the scent is basically dessert marketing.
