1. Preheat oven to 375 and spray a nine-inch round cake pan with cooking spray (and if you have a springform pan it’s perfect for this!)
2. Rinse off your blueberries and let them dry while you are making the batter.
3. Put 4 tablespoons of the butter and 1/2 cup of the sugar in a bowl and beat them together with a mixer for 2 minutes.  Add in the egg and vanilla and beat until combined.
4. Put 1 3/4 cups flour, baking powder and cinnamon in a bowl and stir with a whisk until well combined.
5. Add half the flour mixture, then the milk, then the rest of the flour mixture to the butter mixture, mixing just until blended.
6. Transfer the batter to your cake pan, smooth it out and then pour the blueberries on top.
7. Now make the crumble topping!  Put 4 tablespoons of butter, 1/2 cup of sugar and 1/2 cup of flour in a bowl and mix it up until it is in crumbled (clean hands work best for this!).  Sprinkle the crumble mixture over the top of the cake.
8. Bake the cake for 45 minutes and then let it cool on a rack.

Lemon Sauce

1. Put 2 beaten eggs and 1 cup of sugar in a double boiler (don’t have a double boiler?  See the handy note below).  Don’t turn the heat on yet.  Whisk them up together and add the lemon juice, the lemon zest and 2 tablespoons of butter.
2. Now turn the heat on until the water is simmering.  Whisk it for 10 minutes or so until the sauce starts to thicken up.
3. Now cut that cake into slices, drizzle with the lemon sauce, and dig in!