Heat oven to 350 F. Oil 8-by-12-by-2-inch pan with olive oil and line bottom with parchment paper.
In bowl, whisk flour, sugars, salt, baking soda and powder. In another bowl, whisk 1 1/3 cups olive oil, milk, eggs, lemon zest, juice and limoncello. Add dry ingredients; whisk until just combined.
Pour batter into prepared pan and bake 60-75 minutes until top is golden and cake tester comes out clean. Transfer cake to rack and let cool 30 minutes.
Run knife around edge of pan, invert cake onto rack and let cool completely, 2 hours.
Sprinkle with powdered sugar, lemon zest and lemon rings right before serving, if desired.