In a light-colored heavy-bottomed saucepan, heat the sugar over medium heat, stirring constantly with a heatproof silicone spatula or wooden spoon.
The sugar will start to clump, then gradually melt into an amber liquid. Keep stirring gently to help it melt evenly.
As soon as all the sugar has melted and it turns a deep golden color, remove it from the heat immediately — it goes from perfect to burnt in seconds.
Carefully stir in the butter — the caramel will bubble vigorously. Keep stirring until fully melted and combined.
Slowly pour in the cream, stirring constantly. It will bubble up again; keep stirring until smooth.
Stir in vanilla and salt, if using.
Let it cool for about 10–15 minutes before drizzling over your baked bars — it should still be pourable but not piping hot.
