Grease your donut moulds. I find cake release spray or spray oil works best.
Put the sugar and butter in a large mixing bowl and whisk together until pale.
Add the eggs one by one, whisking as you go.
Add the vanilla, milk, lemon zest and juice and whisk again.
Sift in the flour then fold together.
Pipe and bake.
Transfer the batter to a piping bag and snip off the end to create a 2cm-wide hole. Pipe the batter into the greased doughnut moulds. You have enough for 12 in the donut pan pictured but in smaller/larger or shallower/deeper pans, you may get more/less.
Bake for approximately 30-35 minutes until risen and firm. Transfer to a wire rack to cool completely.
To make the glaze.
Sift the icing sugar into a mixing bowl and add the lemon juice.
Mix to a thick, pourable icing.
Take the completely cooled doughnuts and dip halfway into the glaze, then back on the wire rack to set.