I recently made some pesto from scratch and my end result, while delicious, was overpowered by a strong garlic flavor, and not entirely in a good way. I'm talking about that sharp, spicy flavor that garlic sometimes imparts.  I would have added more basil if I had it on hand, but I used all of my stash in the first go-round.  What else could I add to lessen the flavor?  Is there a general purpose ingredient for this situation? 
I know this is a bit of an old question but I came along it on my own search so thought I'd share my solution.   I figured the problem with the excess garlic is that it's raw so I sprinkled some parmesan on top of my pesto and baked it in the oven for 5-10mins. Stirred through the now melted parmesen with the semi-cooked garlic and it tastes so much better. Still a little garlic-y for my liking but hey, we can't all be perfect.   Oh, I was making my pesto in a glass mixing bowl so just chucked the whole thing in the oven but make sure whatever you have it in is oven safe before whacking it in. Enjoy! 