Preheat the oven to 350°F.
Spray a 9x13-inch baking pan with baking spray.
In the bowl of a stand mixer, add the softened butter and dark brown sugar.
Cream the butter and sugar together until light and fluffy.
Add the molasses and mix until combined.
Add the eggs and vanilla extract.
Mix until the wet ingredients are fully incorporated.
In a separate mixing bowl, sift together the all-purpose flour, whole wheat flour, baking soda, ground cinnamon, ground ginger, ground cloves, and salt.
With the mixer on the lowest speed, add half of the dry ingredients to the butter mixture.
Add half of the buttermilk and mix until just combined.
Add the remaining dry ingredients, followed by the remaining buttermilk.
Mix only until the batter is combined. Do not overmix.
Pour the batter into the prepared baking pan.
Spread the batter evenly into the pan with a spatula.
Break the prepared crumb topping into chunks about the size of marbles.
Scatter the crumb topping evenly over the cake batter.
Bake for 35 to 40 minutes, or until a knife inserted into the center of the cake comes out clean.
Remove the cake from the oven.
Allow the cake to cool before slicing and serving.