This is in no way meant to be an "authentic" mostarda. Purists would perhaps call it a chutney. Call it what you will, it is a delicious accompaniment to cheeses and cured meats (or roasted...
Last summer at the Joy Kitchen, we had a ridiculously large crop of sweet basil to put up around late August. Due to the large scale, we decided to make a freezer-friendly herb butter instead of what most of us usually want to make with basil: pesto. Luckily, we had some volunteer plants from last year that still produced a sizable amount, but not too much to rule out pesto. Still, in order to keep costs down, we opted to use almonds and hazelnuts instead of the now unjustifiably expensive pine nuts for our pesto. While Ligurians would probably scream at this defilement of their world-famous herb paste, we think hazelnuts, almonds, or even walnuts are equally delicious substitutes--either in part or all together--for the ever-pricier pine nut.
We have neither the guts or desire to call for anything but Parmesano Reggiano, though many might be tempted by the Argentine varieties, which serve the purpose well considering their significantly lower price. Gran Padano is a fine, though often less flavorful option. A fairly new cheese to American supermarkets, Piave vecchio (or stravecchio) is a fine substitute and can (for the moment) be found at reasonable prices. If you really have no respect for the whole authenticity thing, a nice aged, extra-sharp cheddar--Tillamook Special Reserve, Grafton Village, Cabot Clothbound-- or an aged Gouda can make for delicious pestos, but you should try experimenting in small quantities before you commit to storing a ton of it.
Since we're on the subject of pesto heresies, remember that arugula is a fantastic substitute for basil if you have no crop to call upon and have to make do with what you can find at a supermarket. So if you do not have a cheap source of basil, arugula is the secret ingredient to use for affordable homemade pesto. It has a nice peppery flavor and stays green longer when exposed to oxygen.
Whereas basil butter is easy to freeze in large blocks and cut unthawed portions off of as needed, pesto--to my mind-- can be frozen and stored in an even more convenient manner: spoon the paste into ice cube trays, cover with plastic wrap and freeze, knock out the cubes into a zip-top bag. One cube can be easily snatched from the freezer and tossed in to a freshly-boiled pot of pasta or dissolved into a batch of minnestrone... no thawing, no chipping, no packaging waste.
If you are dealing with a large pile of basil, pick the leaves, figure out how much you have with a 1-cup measure, and scale up the other ingredients accordingly. For shopping purposes, the amount of basil leaves pictured above (gathered from two full-grown plants) required me to make 6 batches of this recipe.
Combine in a food processor and process to a rough paste:
2 cups loosely packed basil leaves
1⁄2 cup grated Parmesan
1⁄3 cup pine nuts, hazelnuts, almonds, or a combination
2 medium garlic cloves, peeled
With the machine running, slowly add:
1⁄2 cup olive oil, or as needed
If the pesto seems dry (it should be a thick paste), add a little more olive oil. Season to taste with:
Salt and black pepper
Use immediately, or pour a very thin film of olive oil over the top, cover, and refrigerate for up to 1 week. Or, as discussed above, freeze in an ice cube tray, covered. Knock out for storing into a zip-top bag and freeze for up to 3 months. Doubling the recipe will fill up an ice cube tray.