Preheat the oven to 350°F (175°C).
Combine dry ingredients: In a large bowl, mix together flour, sugar, baking powder, and salt.
Mix wet ingredients: In another bowl or a measuring jug, whisk together buttermilk, eggs, vanilla pod seeds, melted butter, and vanilla extract until well incorporated.
Prepare donut pans: Lightly grease standard or mini donut pans with cooking spray or melted butter.
Fill the pans: Pour the batter into the donut pans, filling each cavity about ¾ full.
Bake: Place in the oven and bake for 15-18 minutes, or until the donuts are golden and bounce back when lightly touched.
Cool: After baking, allow the donuts to cool in the pan for about 10 minutes before transferring them to a cooling rack to cool completely.
Make the glaze: In a bowl, combine the icing sugar and milk, whisking until you have a thick glaze. Adjust the thickness with more icing sugar if it’s too thin.
Glaze the donuts: Dip the top of each cooled donut into the glaze, then place back on the cooling rack. If you wish to decorate, do so while the glaze is still wet.