Preheat oven to 350°F. Grease an 8x4 inch loaf pan or line with parchment.
Whisk together almond flour, baking powder, and salt in a medium bowl.
In a large bowl, whisk melted butter, sweetener, eggs, sour cream, lemon juice, lemon zest, and vanilla until smooth.
Fold dry ingredients into wet until just combined.
Pour batter into the pan and smooth the top.
Bake 45 to 55 minutes, until a toothpick comes out with a few moist crumbs.
Tent with foil during the last 15 minutes if the top browns too fast.
Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely before slicing.