Dissolving sugar in a beverage I have a hard time getting sugar to fully dissolve when I'm stirring a cocktail (for example, an old fashioned). I'm using granulated sugar (https://www.dominosugar.com/sugar/granulated-sugar) and I tend to stir a small amount in a shaker with 100+ quick circles and the sugar still hovers in the middle and sits on the bottom without dissolving. What am I doing wrong?
Most cocktails use sugar syrup (e.g. simple syrup with a water to sugar ratio of 1:1 or 1:2) instead of granulated sugar. This eliminates the need to dissolve the grains in - typically cold - liquids.

When you consider powdered (confectioner's) sugar because of the smaller grain size, remember that they will most likely contain anti-caking agents like starch or tricalcium phosphate. I'm not entirely sure how much this would influence the final taste, though.