Preheat your oven to 350°F. Line a small loaf pan (8.5 X 4.5 inches) with parchment paper, leaving overhang, as shown in the video. Lightly spray the parchment paper with oil.
In a medium bowl, whisk the eggs, melted butter, sweetener, and vanilla extract.
Gradually add the lemon zest, almond flour, kosher salt, and finally the baking powder.
Transfer the batter to the prepared loaf pan. Smooth the top out with a spatula and tap the pan a few times on the kitchen counter to help spread the batter evenly in the pan.
Bake the cake until puffed, golden and fragrant, and a toothpick inserted in its center comes out clean. This should take about 30 minutes.
Remove the cake from the oven to a cooling rack. Let it cool slightly until easier to handle, then use the parchment overhang to remove the cake from the pan. Carefully peel the parchment away and place the cake directly on the cooling rack. Cool for 30 more minutes before slicing.
*I use Bob's Red Mill Super-Fine Almond Flour. One cup of this flour weighs 4 oz, so 2 cups weigh 8 ounces. It's best to measure almond flour by weight rather than by volume. It's important to use a small loaf pan. The cake will be flat if you use a standard loaf pan.Leftovers keep well in the fridge, in an airtight container, for up to 5 days. Place the cake on wax paper. You can also slice it and freeze the slices in freezer bags.