Preheat the oven to 400 degrees. Carefully unroll the puff pastry onto a lightly floured piece of parchment paper and roll it out with a floured rolling pin to about a 10 inch by 16 inch rectangle. Poke the pastry all over with a fork. Transfer the parchment to a baking sheet and bake the pastry for about 12 minutes, or until lightly golden and puffed.

Meanwhile, bring a large skillet of water to a boil. Add the asparagus and cook 2-4 minutes, or until they are bright green and have just a little bit of crispness left. Remove the asparagus to a plate and toss with the olive oil, 1/2 teaspoon Kosher salt, and a generous sprinkling of black pepper. Set aside.

Whisk together the ricotta, 1/2 cup Parmigiano-Reggiano, egg, 1/2 teaspoon Kosher salt, lemon zest, and lemon juice. Once the puff pastry has cooled slightly, spread the ricotta mixture evenly over the top, leaving a 1 inch border all the way around. Layer the asparagus stems evenly over the ricotta. Brush the exposed crust with olive oil. Return to the oven and bake for another 15-20 minutes, or until asparagus is tender and crust is golden brown. Sprinkle with remaining Parmigiano-Reggiano and serve.