Preheat the oven to 350°F. Line a standard 12-cup muffin pan with parchment or silicone muffin liners.
Add the almond flour, granulated keto sweetener, poppy seeds, baking powder, and salt to a large mixing bowl. Whisk until evenly combined.
Add the eggs, melted butter, sour cream, fresh lemon juice, lemon zest, vanilla extract, and optional lemon extract.
Stir until the ingredients are completely combined and a thick, smooth muffin batter forms.
Divide the batter evenly between the 12 prepared muffin cups. Fill each cup about two-thirds to three-quarters full.
Bake for 18 to 22 minutes, or until the tops are lightly golden and the centers are set.
Insert a toothpick into the center of a muffin. It should come out clean or with a few moist crumbs.
Allow the muffins to cool in the pan for about 10 minutes.
Carefully transfer the muffins to a wire cooling rack and allow them to cool completely.
To make the lemon glaze, whisk the powdered keto sweetener with 1 tablespoon of fresh lemon juice.
Add additional lemon juice a little at a time until the glaze reaches a smooth, drizzleable consistency.
Drizzle the glaze over the cooled muffins. Allow the glaze to set before serving.
