Begin by preheating your oven to 350°F (175°C). This is an essential step that ensures an even baking temperature. Grease a 9-inch round cake pan, or line it with parchment paper for easy release later.

In a medium bowl, whisk together the flour, baking powder, and salt. Set this mixture aside. This prevents clumping and ensures that your leavening agent is evenly distributed.

In a large mixing bowl, beat the softened butter and sugar together until the mixture is light and fluffy. This typically takes about 3-4 minutes with an electric mixer. The air incorporated during this process helps create a tender cake.

Next, add the eggs one at a time, beating well after each addition. Pour in the vanilla extract and mix until combined. The batter should look smooth and creamy.

Pour in the cooled brewed coffee and sour cream into the butter mixture. Mix on low speed until just combined.

Gradually add the dry ingredients to the wet mixture. Stir carefully using a spatula or wooden spoon just until combined. Avoid over-mixing, as this can lead to a tough cake.

In a separate bowl, combine the cold butter cubes, flour, granulated sugar, brown sugar, cinnamon, espresso powder, and dark chocolate. Use a fork or your fingers to mix until crumbly. It should look like coarse sand.

Spoon half of the batter into your prepared cake pan. Spread it evenly across the bottom. Sprinkle half of the crumb topping over the batter. For an added surprise, mix the brown sugar with espresso powder, and sprinkle that as well. Finally, pour the remaining batter on top balanced by a layer of crumb topping.

Bake the cake in your preheated oven for 35-40 minutes, or until a toothpick inserted in the center comes out clean. It’ll puff up beautifully, with a golden-brown top.

While the cake is cooling, combine powdered sugar, brewed coffee or milk, espresso powder, and vanilla extract in a small bowl. Whisk until smooth. Adjust with more liquid if you like a thinner glaze.

Once the cake is cool, remove it from the pan and drizzle the glaze over the top, letting it cascade down the sides. This is where it gets visually enticing!