A simple and easy to make quick-cake. It'll be a hit at tea or coffee (European times), or as simply a lovely afternoon snack for a hungry teen.
Preheat the oven to 350°F.
Grease (I always use a little lard) and line (if desired) an 8-inch square cake pan. Set aside.
For the crumble; in a medium bowl, combine and dry-mix all the ground cinnamon, brown sugar, salt, and flour. Add the butter. Using your fingers, rub the butter into the flour and sugar mixture until crumbly. Put the crumble mix into the refrigerator.
For the cake; in a small or mixer bowl, cream the butter, sugar and vanilla until light and fluffy. Beat in the eggs one at a time until well mixed. Add the lemon zest and mix just enough to incorporate.
In a larger bowl, dry mix the flour, baking powder, baking soda and salt. Add the buttermilk and gently mix to moisten and completely incorporate the liquid. Finally, gently fold in the blueberries.
Pour this batter into your previously prepared tin. Sprinkle the crumble mixture over the top. Ensure that the batter is completely covered.
Bake at 350°F for approximately 50 minutes or until "the crumble" is golden brown and a toothpick inserted in the middle comes out clean. Allow to cool in the pan for 10-15 minutes before inverting onto a cooling rack.
Dust with icing sugar if desired.