Preheat your oven to 350°F / 176°C and grease a 10" / 26cm pan or line it with parchment paper. If using blanched almonds instead of almond flour, process them in the food processor until they're pretty finely ground. If you grind them too much, they'll release oil and become almond butter.
Combine the white chocolate and milk / cream in a microwave safe bowl.
Heat in 30 second increments and stir after every 30 seconds. Set aside to cool while you prepare the rest. Beat the butter with 100 grams of sugar and beat until fluffy.
Add the lemon zest, egg yolks and lemon extract and beat until well combined. Then add the almond flour / ground almonds and the melted chocolate. Add the limoncello / lemon juice and beat until combined.
In a separate bowl with spotlessly clean beaters, beat the egg whites until soft peaks form. Gradually add the remaining 30 grams of sugar to the egg white mixture. Fold the egg whites into the almond batter until well combined. Spoon the batter into the greased pan and bake for 40 - 45 minutes. If making half the cake, use a 7" / 18cm pan and bake for 30 minutes. The cake will puff up in the oven, but when cooling, it'll fall back down.
Let it cool completely in the pan and then invert the cake onto a plate, and then flip that back into the pan or onto another plate (so that it's not upside down). Sprinkle on some powdered sugar if desired, but only before serving.
If using coconut sugar, blend in a coffee grinder first so that it's basically like powdered coconut sugar. I'd be worried about how well non-grinded coconut sugar would do with the egg whites. I'm guessing not well. And please note the above comment about how using coconut sugar turns the cake the brown! It's just not possible to make a bright yellow cake with this dark sugar. Also, this recipe originally used 200 grams of sugar. I used 200 grams in the first cake and only 130 in the second and didn't notice much of a difference, but I'm used to not using so much sugar. Feel free to use up to 200 grams.