Heat sugar and water in a saucepan over medium, stirring until dissolved. Stop stirring; cook to golden amber.
Off heat, whisk in cream (it will bubble), then butter and salt. Cool to thicken.
Preheat oven to 350°F (175°C). Line muffin tin. Sift flour, cocoa, baking soda, baking powder, and salt.
In another bowl, whisk sugars, eggs, oil, buttermilk, and vanilla. Combine with dry ingredients; fold in chocolate chips if using.
Add 1 tbsp batter to each liner, 1 tsp caramel in center, then cover until 3/4 full.
Bake 16–18 mins, checking side (not center) with a toothpick. Cool 10 mins in pan, then transfer to rack.
Heat cream until simmering; pour over chocolate. Rest 2 mins, then whisk smooth. Cool slightly.
Top muffins with ganache, sprinkle pistachios, and add gold dust if desired.