Grease and line the bottom of a 9" springform pan with parchment paper. Set aside. Heat oven to 350°F.
In a large mixing bowl, combine 4 egg yolks and sugar. Beat with an electric mixer on high speed 2 minutes or until thick, creamy and lightened in color. Add almond flour and lemon zest. Use a spatula to fold and stir together until incorporated.
In a second large mixing bowl, add 4 egg whites and beat until stiff peaks form (about 2 minutes). Fold the egg whites into the almond batter. Be sure to scrape all the way to the bottom and continue folding until there are no more white streaks.
Once all the egg whites are incorporated and batter is even in consistency (do not over-mix), transfer batter to the prepared baking pan. Bake at 350˚F for 30 minutes or until top is firm.
Let cake rest in the pan 15 minutes then run a thin spatula around the sides and invert it onto your hand then place it right side up on the rack.
In a small bowl, stir together the lemon juice and confectioners sugar. Using a pastry brush (or a spoon), brush the top of the cake with the lemon syrup. Use it all up! Sprinkle almond slices, confectioners sugar and lemon slices on top. The confectioners sugar will dissolve into the syrup, so serve immediately or wait to sprinkle with sugar until just before serving.