Preheat your oven to 350°F (175C/155C Fan).
In a medium bowl, cream together your butter and sugar until pale and well mixed. Add the eggs one at a time and whisk together after each. Then add the extracts and zest, whisking to combine.
Add the baking powder, salt and then the flour slowly in three or four additions - mixing to combine after each.
Add the soured milk or buttermilk slowly in several additions, mixing as you go until you have a fully combined, smooth, thick batter.
Add your batter to a piping bag and pipe around twelve donut mould holes. Fill these approximately ¾ full.
Place in the oven and bake for about 20 minutes, until a toothpick inserted in the thickest part of the middle donuts comes out clean. Remove from the oven and allow to cool in the pan for a few minutes if using silicone moulds. Then turn out onto a wire rack to cool while you make the glaze.