Heat the buttermilk slightly in a bowl in the microwave & leave the earl grey tea bags to soak inside the bowl for 10-15 minutes. Stir the tea bags around & when removed from the bowl the buttermilk should be fragrant and tinged slightly brown. (For a weaker taste, leave the tea bags to soak for 5-7 minutes and stir only lightly.)
Preheat the oven to 180C. Liberally grease the bundt tin (We do not want a broken cake after all this work!) with butter & then dust lightly with flour. Set aside.
In a medium bowl, sift together the flour, baking powder, and bicarbonate of soda.
In a different bowl, cream together the butter and sugar until pale & fluffy, about 5 minutes. Add the vanilla extract & beat until well incorporated, about 1-2 minutes.
Add in the eggs, one at a time, making sure it is well incorporated after each addition, being sure to scrape down the sides of the bowl.
Alternate between adding 1/3 of the flour mixture and then ½ of the buttermilk into the batter until everything is incorporated, mixing gently each time until just combined – do not over mix the batter.
Pour the batter evenly into the prepared bundt tin & lightly tap it against a surface to remove any air bubbles. Bake the cake for one hour, until a toothpick inserted into the centre of the cake comes out clean. Invert the finished cake onto a wire rack & leave to cool for another hour.
To make the glaze, mix together the zest & juice of the lemon with the icing sugar in a small bowl until it becomes a paste. Add more or less of each ingredient to get the desired consistency.
When the cake is completely cooled, drizzle with the lemon glaze.