Start with the crumb topping. In a medium bowl, combine the cold, diced butter, muscovado sugar, flour, cinnamon, and nutmeg. Use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs. Set it aside.

Preheat your oven to 350°F (175°C). Grease a 9-inch round cake pan or line it with parchment paper. In another bowl, cream the softened butter and granulated sugar together until light and fluffy. This step adds air, making the cake tender.

Next, incorporate the eggs, adding them one at a time. Mix in the vanilla extract, ensuring everything is well combined and smooth.

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt. Add this mixture to the butter-sugar mixture alternately with the sour cream and milk. Start and finish with the flour mixture, mixing only until combined. A little extra mixing can lead to a denser cake, so take care.

Don’t forget the lemon zest! This tiny touch will elevate the cake’s flavors, adding that extra zing. Fold it into the batter gently.

Pour half the cake batter into your prepared pan. Then, sprinkle half of the crumb topping over it. Pour the remaining batter and then sprinkle the rest of the crumb mixture on top.

Bake in your preheated oven for about 40-45 minutes or until a toothpick inserted in the center comes out clean. Let it cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

If you’re feeling adventurous and want to add a little sweetness on top, whisk together the heavy cream, powdered sugar, and vanilla extract to make the icing. Drizzle it over the cooled cake.