To begin, preheat your oven to 350 and spray two donut pans with non-stick spray.
To a large mixing bowl, add your butter, maple syrup, Greek yogurt, milk, lemon juice, lemon zest, and vanilla and whisk together till well combined. Add your egg and briefly whisk it in.
To the same bowl, add your flour, baking powder and salt and stir together till you have a smooth donut batter.
Scoop or pipe it into your donut pan till 2/3 way full (or to just under the top lip). Bake for 7-9 minutes, or till fluffy to touch or a toothpick inserted comes out clean.
Let cool entirely before removing from pan. For easy removal, slide a butter knife around the edge of each donut. Flip them out onto a cooling rack.
To a small mixing bowl, add 3 tsp of milk, lemon juice, vanilla, and powdered sugar. Whisk till you have a smooth glaze. If needed, add another teaspoon of milk.
Drizzle on top of your donuts or carefully dip the tops of your donuts into the glaze.
Add sprinkles if you'd like and devour!
I recommend storing these in an airtight container in the fridge, where they'll last about a week.