Spray a doughnut pan with non-stick spray and set aside. Preheat oven to 350° F.
In a medium bowl, place flour, poppy seeds, baking powder, salt and baking soda. Whisk together, then set bowl aside. In separate bowl, combine butter, egg, granulated sugar, sour cream, milk, vanilla, lemon zest and juice. Whisk together until batter is smooth, Pour this wet mixture into bowl with dry ingredients. Stir until combined into a thick batter, but make sure not to over mix!
Carefully spoon (or pipe) batter into doughnut pan, filling each cup 2/3 to 3/4 of the way full. If you have a 6 cup pan, you may have to bake these in batches.
Bake doughnuts for approx. 10 minutes. Check them at 9 minutes. The edges should be slightly brown when done. When done, remove pan from oven, and let it sit for 2-3 minutes, then transfer doughnuts from pan to a wire rack that is on top of a piece of parchment paper (when you glaze the doughnuts later, any glaze that drips will land on parchment paper, which is better for easy clean up!). Repeat process with any leftover batter. Once done, let doughnuts cool before putting the glaze on them.
To make the lemon glaze, place powdered sugar, melted butter, lemon juice, milk and vanilla extract in a medium sized bowl. Mix together until you have a creamy glaze. I used 1½ Tablespoons of milk to get it to the consistency I wanted, but if you want the glaze to be thicker, only use 1 Tablespoon milk.
Once doughnuts have cooled, frost with lemon glaze by picking up a doughnut and dipping the top side into the glaze to coat. Flip it over and put the doughnut back on wire rack. Sprinkle with a few poppy seeds, if desired. Repeat until all doughnuts are glazed. Once the "icing" has firmed, doughnuts are ready to serve.
Glazed Lemon Poppy Seed Doughnuts https://www.thegratefulgirlcooks.com/glazed-lemon-poppy-seed-doughnuts/