I use fresh citrus all the time in my recipes- lemon, grapefruit, oranges, limes... and oftentimes the recipes only call for a small amount of zest, or none at all. Well, I won't stand for that! If I'm already getting the microplane dirty, I'm going to zest everything in sight.
It's very simple to take the fresh zest and make citrus sugar. You can mix it with sugar as is after zesting, and the sugar will take on the flavor of the fruit. If you really want to go above and beyond, you can put the mixture in your food processor and really grind up the zest. Your call!
My ratio is 1/4 cup of sugar to 1 T of zest, but you can play with it and see what you like.
What will you use citrus sugar for? Well, everything and anything! I love having it around for cocktails, but you can use it anywhere regular sugar is called for (pretty much) to add some brightness and punch. Dust it on fresh cut fruit, add it to iced tea or lemonade, use it in whipped cream to go with a fruit pie...the options are endless!