I love that no matter how much I learn about food and cooking, it can still surprise me. Last month, after rounds of recipe testing to determine the best way to make a classic pesto sauce, I concluded that using a mortar and pestle made the biggest difference in the quality of the sauce. One might think that a rule like that would therefore apply to all pesto-like sauces. But one who makes such assumptions would be wrong. My proof? This awesome pesto variation I created with mint, feta, and pistachios...well, awesome so long as you avoid the mortar and pestle.
I made this sauce with roughly equal quantities of mint and parsley, since I wanted the flavor of mint, but didn't want the pesto to taste like mouthwash. Parsley helps rein in the mint without competing too much with its fresh smell and flavor.
Then, instead of pesto's traditional pine nuts, I used pistachios here, which is one of my favorite nuts. (It's probably stupid of me to even talk about favorite nuts, since I also claim pecans, cashews, pine nuts, hazelnuts, and almonds as my favorites.) My only warning with pistachios is to keep an eye out for funky brown ones, which are almost always hiding in the mix and can taint the flavor of whatever you're making.
As for the cheese, I added Parmigiano-Reggiano, a classic pesto ingredient, but then turned to feta, a very different sheep milk cheese from the Pecorino Sardo or Romano cheeses commonly used. It has a creaminess that gives great body to the sauce, but I was careful to use only a small amount because it's such a strong, briny, salty cheese—too much feta can lay waste to other flavors.
If I'd been following my own pesto advice, I would have skipped the blender and made just one batch of this in a mortar and pestle. But a voice in my head was telling me to try it both ways. The blender version (I used an immersion blender) is pictured above. It came out great. As for the mortar and pestle version, I'll show you:
I started by crushing the pistachios and garlic. In my classic pesto recipe, I added the pine nuts after the basil, because I wanted to be sure I could completely crush the basil, and knew the soft pine nuts would be easy enough to squash after that (logic being that the ingredients that go into a mortar first crush more easily against the stone surface, while ingredients added later have to contend with the padding of all the food that's already in there). Here, I did the nuts first, because I knew they would be difficult to pulverize, and then figured I'd work the herbs in after that. This was the first problem: Pistachios are a lot more rugged than tender pine nuts, and working them into a paste is not easy, even when they go in early.
This was about as fine as I got the nuts before I gave up and moved on to adding the herbs.
Working in the herbs wasn't easy either—mint and parsley leaves are much tougher than basil leaves. No matter how hard I worked, I just couldn't break them down well enough.
Eventually, I gave up and added the cheeses, then tried to work in the oil. Warning, this isn't so appetizing...
Yeah, I think this might be where Swamp Thing lives.
After this failure, I took the blender to it and all was well. So, heed my advice and don't bother breaking out the mortar and pestle for this one. The blender or food processor will be much faster and give you far better results.
As for serving, this pesto is, of course, great on pasta, though its richness and flavors make it fantastic on sliced tomatoes, boiled potatoes, and meats like chicken, pork, or lamb.