Step 1

Preheat the oven with a rack in the middle to 350°F (180°C). Grease a 9-inch ring mold pan with neutral oil.

Step 2

In a medium bowl, whisk together the flour, baking powder, salt, and lemon zest.

Step 3

In a separate large bowl, whisk together the sugar and eggs until the sugar dissolves and the mixture turns slightly bubbly, 2 minutes. Add the oil, milk, limoncello, sourdough starter, and vanilla. Whisk vigorously until everything is combined and the mixture becomes frothy. Add the flour mixture and stir with a rubber spatula until just combined (avoid overmixing). Pour the batter into the prepared pan. Place the pan on a sheet pan.

Step 4

Bake until a knife inserted into the cake comes out clean, 40 to 45 minutes. Remove the pan from the oven and let cool for 10 minutes. Use an offset spatula or knife to gently release the edges of the cake from the pan, turn the cake out onto a wire rack, and let cool. Once completely cool, dust the top with powdered sugar (if desired). The cake will keep well for several days on the kitchen counter, covered.