Can you substitute powdered sugar? It is for a mud cake recipe.
I wouldn't substitue it.
They're completely different textures and I don't know how it would affect the cake.
Of course, I'll watch this thread with interest....
You can make caster sugar by putting regular sugar in a food processor and pulse a few times. I have done this many times and it works fine.
Caster sugar has a finer grain (0.35 mm) than standard sugar (0.5 mm grain size). Powdered/confectioner's sugar as a finer yet grain (0.060 mm) and contains 1-3% cornstarch as an anti-clumping agent.
If you don't have caster sugar, put the regular sugar in a blender or food processor and pulse a few times.