Sometimes when I melt chocolate in a double boiler it will turn grainy, and melting in a microwave often burns it. What is the best way to melt chocolate to get good, smooth results?
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.
Melting chocolate in a double boiler is the safest method for melting chocolate, and it's fairly easy. But it makes two pots dirty. I didn't had the problem of it being grainy. So I don't know what to say about that.
Melting chocolate in the microwave oven is faster and requires less dishes, but you have the risk of burning. Therefore, lower the wattage and take it out to stir every 20 seconds. It also continues to melt out of the microwave oven, so you can take it out even when there are still some pieces. They will melt because of the heat of the surroundings. If you see that not everything is going to be melted, pop it back in for ten seconds and stir.
I would advice using the microwave oven (but with reduced power), although most chefs (in their videos at least) use a double broiler.
And a footnote: be very careful with white chocolate. That tends to burn the most easily.
If you are very patient, and chop the chocolate into reasonably small pieces (say a 1/2 inch squares), or use chocolate chips, the microwave at low power is extremely effective.
I put chocolate in on power level 2 on mine -- it takes several minutes at that low level -- and you should stir several times. I do this in a glass bowl, intentionally, so there will be some residual warmth when I take it out. At low power, the risk of burning is insignificant.
By doing this, I can keep chocolate in temper for candy (12 ounces of chocolate and three cups crunchy cereal like corn flakes is wonderful) without all the usual fuss of tempering.