Preheat oven to 350°F (175°C). Grease and flour an 8x8 inch baking pan with almond flour.

In a large bowl, whisk together almond flour, granular sweetener, whey protein powder, baking powder, and salt. In a separate medium bowl, whisk together eggs, melted butter, lemon zest, and lemon juice.

Pour the wet ingredients into the dry ingredients and mix until just combined. Pour the batter into the prepared baking pan and spread evenly. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Once the cake is baked, let it cool for 10 minutes. While still warm, use the handle of a wooden spoon or a skewer to poke holes all over the cake.

Gently warm the keto lemon curd (if it's too thick) and then pour it evenly over the warm cake, ensuring it seeps into all the holes. Spread any excess over the top. Let the cake cool completely before serving.