Wrap the ricotta cheese in a cheese cloth, then place in a colander set over a large bowl. Weigh the ricotta down with something heavy to press out excess water. Allow to drain for 8 hours or overnight. Skipping this step will result in the gnudi falling apart during cooking.
In a large bowl, combine ricotta, Pecorino Romano, flour, large egg yolk, Kosher salt, and black pepper. Use a spatula to thoroughly mix. Transfer the bowl to a fridge to chill.
Line a rimmed sheet pan with parchment paper, then dust with flour.
Divide the mixture into thirds, then roll each portion into a log. Use a bench scraper to cut the gnudi into 1-inch long pieces, yielding about 10 gnudi per rope. With lightly floured hands, gently roll each gnudi into a uniform ball, then place onto the flour lined baking sheet.
Dust the remaining flour on top of the formed gnudi, ensuring they’re evenly coated on all sides. Transfer the prepared gnudi to a refrigerator to chill.
While the gnudi are chilling, bring a large pot of water to a boil, then season generously with Kosher salt. Add the asparagus and peas, then cook. Use a slotted spoon or spider to transfer to an ice bath to stop the cooking process.
Melt butter in a large skillet over medium heat until it turns golden brown. Add 2 sprigs of sage leaves, if using, then cook. Remove the sage. Add the blanched asparagus and peas, then season with Kosher salt. Lower the heat until the gnudi are cooked.
Carefully lower the gnudi into the simmering water, then cook until they float to the surface. Use a slotted spoon to immediately transfer the gnudi to the prepared sauce. Do not discard cooking water.
Sauté the gnudi in the sauce over medium-high heat, adding reserved cooking water and swirling the pan gently to coat the gnudi without breaking them. Spoon a few of the gnudi onto individual plates, drizzling more of the sauce on top.
Serve immediately with a drizzle of olive oil, grated Parmesan, lemon zest, additional freshly ground black pepper, and a pinch of flaky sea salt.