Measure all ingredients. NOTE: Always spoon lightly and level flour to prevent too much flour and keep the cake light.
Mix together topping ingredients-sugar, flour, cinnamon (and nuts, if using). A mini food processor is helpful for this step, but not necessary. Cut in butter until topping is crumbly.Set aside until ready to add topping.
Butter 9 x 9 baking dish. TIP: If you want to be able to lift it out for serving, line it with 2 pieces of parchment paper to cover all sides and long enough to lift out after baking.
In separate bowl, mix together flour, salt and baking powder with a whisk.
In a large mixing bowl, add softened butter and sugar and cream together with a mixer.
Add egg and and mix into creamed mixture. If using lemon zest, mix into creamed mixture.
Alternately add milk and flour mixture until just combined. Don't over mix.
Fold in blueberries by hand.TIP: Feel free to coat the blueberries in flour which helps them not sink as much. Don't defrost frozen blueberries.
Pour into greased baking dish and sprinkle with topping.
Bake for 40 or so minutes until lightly browned and cake tester or toothpick comes out clean. Be careful not to over bake.
OPTIONAL: Serve warm with fresh whipped cream.
Notes
This recipe is delicious served with a fresh cup of coffee or tea. Try serving it warm with a bit of fresh whipped cream. Great for a morning or afternoon gathering with friends. Although I have used a square baking dish, Marie always used a round cake pan. Feel free to use either.