Panisses with Sage Leaves and Lemon

Pour 2 Tbsp. oil into an 8x8" baking pan; set aside. Bring a pinch of kosher salt and 4 1/4 cups water to a boil in a medium saucepan. Whisking constantly, gradually add chickpea flour. Once all the flour has been incorporated, reduce heat to low and cook mixture, whisking often to prevent scorching and to keep a skin from forming on top, until a thick lumpy porridge forms that is just starting to pull away from the sides of the saucepan, 20–25 minutes.
Transfer mixture to a food processor (keep saucepan close at hand) and process until smooth and very glossy, about 45 seconds. Working quickly so mixture does not start to set, transfer back to saucepan, season with more kosher salt, and cook over low heat, whisking often to prevent any new lumps from forming, until you can see the bottom of pan while whisking and mixture no longer tastes raw, 10–15 minutes.
Scrape mixture into prepared pan and quickly smooth top. Drizzle 1 Tbsp. oil over and cover with a sheet of parchment paper. Let cool, 1–1 1/2 hours (you can speed this up by chilling mixture until cold).
Using the tip of a knife, slice mixture on an angle into 12 irregular strips of varying lengths and thicknesses. Heat remaining 1 1/2 cups oil in a medium skillet, preferably cast iron, over medium-high until the first wisp of smoke appears. Working in 2 or 3 batches, fry strips (if panisses are not submerged in oil, add more just to cover), turning several times, until puffed, crisp, and golden all over, about 5 minutes per batch. Transfer panisses to paper towels to drain and sprinkle with sea salt.
Add sage to skillet and cook just until crisp, about 10 seconds, then transfer to paper towels to drain.
Top warm panisses with sage and serve with lemon wedges.
Panisse mixture (before cutting) can be made 1 day ahead. Cover and chill.