Preheat oven to 160°C and line a round cake tin (springform) with parchment paper en grease the sides.
Beat the butter and sugar until creamy.
Add eggs and lemon extract and beat until well combined. It may look a bit curdled, but that’s all right.
Sift flour and baking powder on top and mix with a rubber spatula until combined. Do not overmix.
Carefully fold in 2/3 of the blueberries.
Pour batter into prepared cake tin and divide the rest of the blueberries on top.
Put the ingredients for the crumb layer in a separate bowl and mix with your hands until you it starts to come together.
Divide the crumbs and bake the cake for ca. 50-60 minutes.
Let cool completely.
Mix the ingredients for the glaze and pour over the cooled cake.
Then serve and enjoy!
* You can use frozen blueberries instead of fresh. To prevent too much juice leaking into the cake, you can coat them in flour. Put the frozen blueberries in a plastic bag, add 1/2-1 tbsp flour, close the bag and gently shake the bag until all berries are covered in flour.