Toast the walnuts over medium heat stirring constantly for 3-5 minutes or until they begin to brown.
Add fennel fronds, lemon juice, salt, half of the olive oil, and nuts to a food processor and blend. Stop and scrape down sides. Continue blending and slowly add remaining olive oil until desired consistency is reached.
Store in an airtight container in fridge and add to pasta, sandwiches, or anywhere else you'd use a normal pesto!
Notes
Freeze: To freeze that freshness, fill a tray like this until the cubes are solid, before transferring them to a freezer-safe bag until you're ready to use, for up to 6 months.Use: To use defrost by either thawing in the fridge before using to loosen, or you could add a cube straight to your hot dish and let it melt right in, like pasta or even as added flavor to your favorite soup!