Preheat the oven to 350 degrees.
Butter a round 9-10 inch spring-form pan and cover the bottom with parchment paper.
Place the almond flour and sugar into the food processor and pulse until finely ground. Add the four eggs to the mixture and pulse until well combined.
Add the vanilla extract and salt and then drop in chunks of the softened butter. Add the zest of 1 lemon and then cut it in half and carefully squeeze the juice making sure you don't let any seeds escape into the batter. Pulse until well combined and smooth.
Pour the batter into the cake pan. Place the rack in the middle of the oven and bake for 30-35 minutes. The top will turn slightly golden and the cake will feel springy to the touch. A toothpick should come out clean when inserted into the cake.
Remove the cake from the oven and let it cool for 10-15 minutes. Unmold the cake, invert onto a plate and remove the parchment paper. Now get a nice plate and invert the cake again so the top of the cake is now right side up.
Using a sieve of sorts, sprinkle confectioners sugar over the top of the cake to make it look even more stunning. Slice and serve with fresh fruit, berries and/or whipped cream.