Preheat the oven to 350℉/180℃ Fan. Grease/Line an 8 inch round cake tin (I use a springform one).
Start by making the crumb topping. Combine all ingredients (Unsalted butter, both sugars, flour) in a small bowl and place in the fridge while you make the cake batter. It should be 'crumbly'. If it feels too paste-like, add more flour, a tablespoon at a time until it's still sticky but able to be crumbled. In a large bowl/bowl of a stand mixer, add all the cake ingredients and combine until smooth. If very stiff, add a little more cream.
Pour the cake batter into the lined tin.
In a bowl, combine the blueberries with the lemon juice, flour and sugar. Pour these blueberries over the cake batter.
Finally, sprinkle the crumb topping over the cake.
Bake 60 minutes. Check that it is completely baked by inserting a skewer - if it comes out clean, it's ready to come out. If not, let bake for 5 minutes more at a time, testing in between. Let cool on a wire rack.
Once the cake is cool, mix together the glaze and drizzle over the cake. Dust with a little more powdered sugar if you like! Slice and serve.