Preparation

Make the filling

• In a bowl, blend both cheeses, the nuts, 1/4 tsp. black pepper, and lemon zest. Squeeze on the lemon juice, taste, and add more juice if you like. Spoon the mixture into a pastry bag, if using.

Stuff the blossoms

• Use your fingers to gently open the blossoms from the tip, taking care not to tear the petals. With the pastry bag, or using a spoon, fill each blossom with the cheese mixture. Don’t overstuff them; they shouldn’t expand like a balloon. Just put in enough cheese so they are filled from base to tip. When each blossom is filled to the top, gently roll the blossom on a work surface to evenly distribute the cheese inside.
• In a small bowl, whisk together the egg yolk and milk. Set aside. Pour the cornmeal onto a small plate and add a pinch of salt, mixing with a fork.
• Dredge a stuffed squash blossom in the egg wash and then in the cornmeal. (See Using the Wet-Hand/Dry-Hand Method of Breading, below.) Repeat with the remaining squash blossoms, adding more cornmeal to the plate if needed.
• Pour enough peanut oil into a 10-inch or larger skillet or saucepan so that you have about 1/2 inch of oil. Heat the oil over medium-low heat until the oil registers 220°F on a deep-fat thermometer. (You don’t want too high a flame, or the cheese will weep and melt too quickly.) If you don’t have a thermometer, test if the oil is ready by tossing a few cornmeal grains into the pan. If the oil sizzles, it’s hot enough.
• These cook quickly. Cook until the cornmeal becomes lightly crisp and golden, for no more than 30 seconds. Transfer to a plate to cool just for a few minutes while you dress the salad.

Make the salad

• In a small bowl, make a dressing by whisking together both vinegars, the olive oil, and 1/2 tsp salt. Season with pepper. Put the mizuna in a medium bowl. Lightly dress the greens and mound equal amounts on four plates. Add a squash blossom and a slice of levain toast to each plate, and serve immediately.