Preheat the oven to 180 º C.
Mix the milk with lemon juice. Set aside.
In a bowl, mix flour, baking powder, and poppy seeds. Set aside.
In the mixer, beat the butter, yellow sugar, orange and lemon zests, and vanilla essence for about 5 minutes.
Add the eggs, one by one, until they are fully incorporated.
Lower your mixer's speed setting to the minimum. Alternate between adding the milk and the dry ingredients until you have a smooth mixture.
Pour this mixture into a bundt cake pan of about 25 cm in diameter, previously greased and dusted with flour.
Bake for about 40 to 45 minutes, or until a skewer inserted in the cake comes out dry.
Let the cake cool down for about 10 minutes. Then invert onto a serving plate. Dust with powdered sugar.