Preheat the oven to 350F (180C) and place the rack in the middle of the oven.
Butter an 8-inch (20cm) square mold with removable sides.

The crunch:
Put all the ingredients except the nuts in a food processor and pulse until the mixture forms small balls of dough, the size of small peas.
Mix in the chopped nuts and combine well.
Refrigerate until use.

For the cake:
In a bowl, mix the blueberries and coat them well with 2 teaspoons of flour. Set aside.

In another bowl, mix the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.

In the mixer bowl, cream the sugar, lemon zest, and butter until the mixture is smooth and light.
Add the eggs one at a time, then the vanilla extract and mix well.

Add the dry ingredients alternately with the buttermilk and mix well.
Gently fold in the blueberries with a spatula.

Pour the preparation into the reserved mold, then sprinkle the crunch mixture evenly over the top.

Bake for 55 to 65 minutes or until the top of the cake is golden brown and a toothpick inserted in the center comes out clean.

Let cool on a rack before slicing.