Chocolate – the best and fastest way to liquify Nutella chocolate spread

It depends on what you're doing with the chocolate.

If temperature isn't that critical and its going to be mixed into a cake or brownies or such, then do it in the microwave. Its simpler and as long as you don't rush it, its does a good job. Just go 10-20 seconds at a time, in bowl that doesn't hold heat well.

If you need precise temperature controlled chocolate (for tempering perhaps), its best to use a double boiler. The bottom pan just has steaming water - so I never really count that as a dirty dish. With the double boiler, you get several advantages. It won't get any hotter than the water. It its gradual and gentle. And you can monitor and stir as the temperature rises. If it turns grainy, its likely a bit of water dripped in. Depending on the top bowl on the double boiler, its possible to accidentally knock some condensation into the chocolate...and now its toast. I use a top bowl that has a small outer lip on it to keep this from happening.

Speaking from making fudge, I have gotten the most consistent results using superfine / castor sugar.

• I haven't noticed starch related issues from powdered sugar, but your mileage may vary; the problem I have had with it is due to clumping in spite of the starch (particularly in a frosting recently).
• I have used granulated sugar to make fudge and it is grainy. I melted most of it, but got sick of stirring it as it got crazy thick. I suppose it's possible to get it to the point of a completely dissolved syrup, but that would take longer than it is worth since you are likely going to run the risk of scorching.

Relative to the taste and structure, you won't get anything special from the caster sugar. However, you will get a more predictable product, and less hassle waiting for it to dissolve. You will also avoid texture problems and reduce the risks brought on by extended time in the pot (i.e. too much heat, likelier to accumulate moisture randomly).