FOR THE CRUMB TOPPING: – 1 cup (120g) all-purpose flour – 1/4 cup (50g) packed light brown sugar – 1/4 cup granulated sugar – 1 teaspoon ground cinnamon – 6 tablespoons (85g) unsalted butter, melted FOR THE COFFEE CAKE: – 1 & 1/4 cups (150g) all-purpose flour – 1 teaspoon baking powder – 1/2 teaspoon baking soda – 1/2 teaspoon salt – 2/3 cup (150g) unsalted butter, softened – 1 cup (200g) granulated sugar – 2 large egg – 1 teaspoon vanilla extract – 2/3 cup Greek yogurt – 1/2 cup (85g) dark chocolate, melted