Preheat oven to 325℉. Line a round 8-inch cake pan with parchment paper. To make the crumble topping, combine butter, vanilla, sugars, cinnamon, flour and salt until no dry flour remains. Set aside.
To make the cake, in a medium bowl, stir together the flour, baking powder, baking soda and salt. Set aside. Add the zest and sugar to a large bowl and rub together with your fingers until the sugar is moist and fragrant. Add the honey and butter and whisk or beat until combined.
Add the eggs, vanilla and yogurt and mix until well combined. If your batter is curdled, that's ok! This is because of the liquid to fat ratio. Add half of the buttermilk, orange juice and flour mixture and mix just until combined.
Add the remaining buttermilk, juice and flour mixture and mix again just until combined. Pour into prepared pan and top with the crumble. Bake for about 35-40 minutes or until a toothpick inserted into the center comes out clean. Let the cake cool for a few minutes before transferring to a cooling rack.
Once the cake has cooled off a bit, top with a dusting of powdered sugar and slice. Serve warm and enjoy!