Last fall Julia taught me the trick of freezing your kale stems after you've torn the greens off. You can then later grind the kale stems into pesto. Use the whole leaf! The pesto is a bit icy if you use the kale stems straight from the freezer and serve it immediately, which can be nice for a cold bean salad in summer. Otherwise, plan to let the pesto warm up to room temp before serving.
Kale stem Walnut Pesto
a bunch worth of frozen kale stems
a handful of walnuts, toasted
1-2 garlic cloves
Throw everything into a food processor and blend. Add olive oil until you're happy with the consistency. Yesterday, I also added a few mint leaves to enliven the flavor a bit.