Step 1

Preheat oven to 350 degrees F.

Step 2

Grease a 9 inch spring-form pan.

Step 3

Mix together both the blueberry filling ingredients and the topping ingredients in separate bowls and set each aside.

Step 4

In one bowl sift together the flour, baking powder, and baking soda.

Step 5

In another medium sized bowl, cream together the butter and sugar until soft and fluffy, about 5 minutes.

Step 6

Add the eggs, beating after each one, and then add the extract and grated lemon zest.

Step 7

Reduce mixer speed to low, and add half the flour mixture, then half the yogurt (or sour cream).

Step 8

Add the rest of the flour mixture and yogurt and beat just until smooth.

Step 9

Spoon half the batter into the prepared baking pan, then add the blueberry filling spreading it evenly across the batter.

Step 10

Top the filling with the rest of the batter, using a spatula to smooth it over the filling.

Step 11

Sprinkle the top of the cake with your walnut and sugar mixture.

Step 12

Bake for about an hour, or until a cake tester comes out clean.

Step 13

Cool to room temperature before removing pan.

Step 14

The cake keeps well for several days wrapped or it can be frozen for several months.