Place ricotta cheese in a small mixing bowl with grated Parmesan, egg yolk, chopped sage, fresh lemon zest, Kosher salt, and black pepper, then stir until well mixed. Transfer the filling to a medium Ziploc bag.
Cut off the tip from one corner of the bag, then insert carefully into the squash flower. It's ok if the leaves rip a little, simply press them gently around the filling. Place stuffed squash blossoms in a refrigerate.
Before you begin dredging, preheat enough neutral oil in a cast iron skillet over medium-high heat to coat the bottom with oil. Look.
In a shallow bowl, whisk together flour and Kosher salt. Pour club soda on top, then whisk until there are no lumps. Dip the stuffed squash blossoms in batter.
We like to fry. Cook per side, using tongs to flip as needed. Once golden brown, transfer to a paper towel lined wire cooling rack. Sprinkle immediately with a pinch of flaky sea salt and additional lemon zest. Cool slightly, then serve!