Prepare the Cake

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9-inch square baking pan.
2. Mix Dry Ingredients: In a large mixing bowl, whisk together flour, sugar, baking powder, ginger, cinnamon, nutmeg, and salt until well combined.
3. Combine Wet Ingredients: In a separate bowl, whisk together the oil, buttermilk, eggs, and vanilla extract until smooth.
4. Mix Batter: Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
5. Pour into Pan: Pour the batter into the prepared baking pan, spreading it evenly.

Prepare the Crumb Topping

1. Combine Topping Ingredients: In a small bowl, mix together the flour, brown sugar, ground ginger, and cinnamon.
2. Cut in Butter: Add the cold butter and use a fork or pastry cutter to blend until the mixture resembles coarse crumbs.
3. Sprinkle Over Cake: Evenly sprinkle the crumb topping over the cake batter in the pan.

Bake the Cake

1. Bake: Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted in the center comes out clean.
2. Cool: Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.