Cream butter and sugar with an electric mixer until light and fluffy.
Add eggs one at a time, beating well after each addition.
Add milk, vanilla, and lemon juice. Stir until well-incorporated.
Stir in baking soda.
Add flour ½ cup at a time.
Stir in blueberries with the mixer on low. It's fine if some blueberries get crushed.
Transfer the batter to a large piping bag. (Tip: Place the bag in a large glass to keep it upright while you transfer the batter to the bag. It's a lot less messy that way!)
Pipe batter into the donut pan, filling compartments about ¾ of the way.
Bake for about 10-12 minutes or until donuts are golden and a toothpick comes out clean.
Remove donuts from the pan and let cool on a wire rack. Let donuts cool completely before dipping in glaze.
Make the glaze by whisking together powdered sugar, heavy cream, and lemon extract.
Dip each donuts in the glaze.
Notes
If the glaze seems too runny, add more powdered sugar. If it seems too thick, add a little more heavy cream.