1.  Preheat oven to 350 degrees. Line a spring form or cake pan with parchment paper, spray it with nonstick cooking spray or lightly butter and flour the pan to prevent sticking.

2.  Break the white chocolate into chunks and add them to a food processor along with both of the flours, salt, sugar and lemon zest. Pulse the ingredients until the chocolate is chopped into fine pieces and is evenly distributed throughout the mixture.

3.  Add the baking soda and baking powder to the mixture in the food processor and pulse another 2 - 3 times.

4.  Transfer the mix to a large mixing bowl (or the bowl of an electric mixer).

5.  To the bowl, add the eggs, olive oil, lemon juice, limoncello and vanilla. If mixing by hand, use a whisk to mix the ingredients thoroughly into a smooth batter. If mixing electrically, mix on medium speed until all ingredients are incorporated and a smooth batter is formed.

6.  Pour the batter into the pan, and then place the pan into the oven on the middle rack. Bake for 45 - 55 minutes or until the cake is golden brown and a toothpick inserted into the center of the cake comes out clean.

7.  When it is finished baking, remove the cake from the oven and let it cool for at least 30 minutes prior to serving. Dust the top of the cake with powdered sugar for decoration if desired.