Heat the oven to 350°F (175°C). Grease an 8- or 9-inch square baking pan and line the bottom with parchment, leaving enough paper over the sides to help lift the cooled cake.

Make the crumb topping by stirring together the flour, brown sugar, cinnamon, and salt. Add the melted butter and mix until large, uneven crumbs form; refrigerate the crumbs while preparing the batter for a crisper topping.

Whisk the cake flour, baking soda, cinnamon, ginger, cloves, and salt in a separate bowl. Breaking up any lumps now helps the spices distribute evenly throughout the cake.

Beat the softened butter and brown sugar for about 2 to 3 minutes, until the mixture is light and smooth. Scrape the sides and bottom of the bowl so the butter is evenly creamed.

Beat in the molasses, egg, and vanilla. The mixture may look slightly curdled, which is normal and will smooth out when the dry ingredients and buttermilk are added.

Add the dry ingredients in three additions, alternating with the buttermilk in two additions. Mix only until the batter is combined, stopping promptly to avoid developing too much gluten.

Spread the batter evenly into the prepared pan. Scatter the chilled crumb mixture over the surface, keeping the crumbs in a generous, even layer.

Bake for 35 to 42 minutes, until the center springs back lightly and a toothpick inserted into the cake comes out with a few moist crumbs. Avoid baking until the toothpick is completely dry.

Cool the cake in the pan for at least 20 minutes before slicing. Use the parchment to lift it out if desired, then cut it into 9 pieces and serve warm or at room temperature.