Preheat the oven to 350°F and lightly grease a mini doughnut pan (I used non-flavored cooking spray).

Sift flour, baking powder and baking soda into a large bowl. Whisk in sugar and sea salt, then set aside.

In a medium bowl, whisk together butter, buttermilk, vanilla, egg and lemon zest until well combined. Add the liquid mixture to the bowl with the dry ingredients, stirring just until combined. Do not overmix here. If the mixture looks a little on the thick side, stir in a splash of buttermilk to loosen it up a bit.

Fill the wells of the mini doughnut pan 3/4 of the way with batter. I used a pastry bag here, but you could also do this with a spoon. Bake until the doughnuts spring back when touched (6 - 8 minutes), and the bottom of the doughnuts are lightly golden (the side that's cooking in the well). Let the doughnuts cool for 2 minutes in the pan, then transfer to a rack to cool completely. Wipe the doughnut pan clean and re-grease before making another batch.

While the doughnuts are cooling, prepare the glaze. In a small bowl, whisk together confectioners' sugar, lemon juice and buttermilk until smooth. Dip one side of each doughnut into the glaze, then place back on the cooling rack. I set my cooling rack over a baking sheet to catch any drips. Sprinkle each glazed doughnut liberally with yellow sanding sugar.