Preheat the oven to 180 degrees C. Grease and flour a 22cm ring tin.
In a large bowl cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time then stir in the lemon essence.
Combine the flour, baking powder and lemon zest then stir into the batter alternating with the milk. I like to use a spatula and stir by hand mixing just until blended so the batter is not over mixed. Be sure to scrape the bottom and sides of the bowl often. Fold in the blueberries. Spoon the batter into the prepared tin.
Bake for 1 hour in the preheated oven or until a toothpick inserted into the centre comes out clean.
Let cool in the tin for at least 10 minutes then invert onto a wire rack to cool completely.