Lemon-yogurt-crumble coffee cake

For Crumble topping:

1. 1/2 cup sugar
2. 1/4 cup all purpose flour
3. grated zest of one lemon
4. 3 tbsp butter, cut into small pieces

Cake:

1. 2 cups all-purpose flour
2. 1 & 1/2 tsp baking powder
3. 1/2 tsp baking soda
4. 1/4 tsp salt
5. 1/4 cup finely chopped candied lemon peel
6. 1 stick unsalted butter
7. 1/4 cup sugar
8. 1 cup plain yogurt of buttermilk
9. 2 eggs, lightly beaten
10. grated zest of one lemon
11. 1 tsp vanilla extract

To make:

1. Preheat oven to 350F. Grease and lightly flour a 9x5 loaf pan, combine the crumble topping ingredients in a small bowl and rub in the butter using your fingertips, until the mixture resembles coarse crumbs; set aside
2. Sift the flour, baking powder, baking soda and salt into a large bowl. Stir in the candied lemon peel and make a well in the center.
3. Put the butter in a saucepan and set over low heat until melted, stirring occasionally. Remove from heat and whisk in the sugar, yogurt, eggs, grated lemon zest and vanilla extract. Pour into the well and stir with a form until just blended.
4. Spoon half the batter into the prepared pan, smoothing the top and pushing into the corners. Sprinkle over half the crumb topping. Drop spoonfuls of the remaining batter over the topping , and spread as evenly as possible, then sprinkle with the remaining topping
5. Bake until the cake is risen and golden, and a cake tester (I use toothpicks) inserted in the center comes out clean, about 1 hour. Remove to a wire rack to cool for at least 30 minutes. Run a thin bladed knife around the edges to loosen it and remove from pan and let it rest on a wire rack to cool.