Set your oven to as low of a temperature as possible. In other words, play "how low can you go?" with your oven. Mine goes down to 170. Alternatively, get your dehydrator ready.
Slice peeled cloves of garlic as thinly as possible, trying to get them all about the same thickness. The thinner you slice them, the faster they'll dry out.
Place on a parchment paper lined cookie sheet, making sure the slices don't touch each other.
Dehydrate until dried (I did mine overnight in my oven).
Take dried pieces of garlic and dump them into your blender/food processor. Grind to desired texture--a more coarse grind will be like granulated garlic. A more fine grind will be like powder. Store in an airtight jar. Use in any dish calling for garlic.