Preheat the oven to 350°F (175°C). Grease a 9-inch springform pan with the 1 tsp softened butter and line the base with parchment.
In a large bowl, combine the granulated sugar and lemon zest. Rub them together with your fingertips until the sugar is fragrant and slightly damp, 30–60 seconds.
Add the 0.5 cup softened butter to the lemon sugar and beat with a hand mixer (or stand mixer) on medium speed until pale and creamy, 2–3 minutes.
Add the ricotta and beat until very smooth and fluffy, 1–2 minutes, scraping the bowl as needed.
Beat in the eggs one at a time on medium speed, letting each incorporate before adding the next, about 30 seconds each.
Mix in the vanilla extract and lemon juice just until combined.
In a separate bowl, whisk together the flour, baking powder, and fine sea salt. Add the dry ingredients to the wet and fold with a spatula just until no dry streaks remain; do not overmix.
Scrape the batter into the prepared pan and smooth the top. Tap the pan once on the counter to release large air bubbles.
Bake until the top is golden and a tester inserted in the center comes out with a few moist crumbs (not wet), 45–55 minutes. If browning too quickly, tent loosely with foil after 35 minutes.
Cool on a rack for 15 minutes, then run a thin knife around the edge and release the springform ring. Cool until barely warm or room temperature, 30–45 minutes more.
Dust the top with confectioners' sugar, slice, and serve.