Preheat the oven to 180C. Grease a 10-cup bundt tin with butter – being sure to get into every little crevice – and set aside.
In a medium bowl, sift together the flour & the baking powder; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the butter, sugar and zest until pale in colour, about 3-4 minutes.
Add the eggs into the bowl one at a time, ensuring each is fully combined before adding the next. Scrape down the sides of the bowl between each addition. When all the eggs have been added, mix in the vanilla extract.
With your mixer on low, gradually beat in half of the flour mixture until just combined. Give the sides of the bowl a good scrape down, then gradually beat in the milk. The mixture will look slightly curdled, but don’t panic! After another scrape down of the sides, at the remaining flour & beat until mostly incorporated.
Scoop the batter into the prepared bundt tin and smooth out the top. Bake in the preheated oven for 45-55 minutes, or until a skewer inserted into the centre of the cake comes out clean. Leave the cake to cool in the tin for 10 minutes before transferring to a wire rack to cool completely.
While the cake cools, make the glaze. Sift the icing sugar into a small mixing jug & use a fork to incorporate the blood orange juice, it should make a smooth icing that isn’t too runny.
Pour the glaze over the cooled cake & leave to set.