Preparation:

Step 1: Preheat the oven and prepare the pan. Preheat your oven to 325°F (165°C). Grease a 10-inch bundt pan or tube pan generously with butter, and dust with cocoa powder to prevent sticking.

Step 2: Mix the dry ingredients. In a medium bowl, sift together the all-purpose flour, cocoa powder, baking powder, baking soda, and salt. Set aside.

Step 3: Cream the butter and sugar. In a large mixing bowl, use a hand or stand mixer to cream the softened butter and granulated sugar together until the mixture is light and fluffy. This should take about 3-4 minutes.

Step 4: Add the eggs and vanilla. Beat in the eggs one at a time, ensuring each egg is fully incorporated before adding the next. Mix in the vanilla extract.

Step 5: Incorporate the dry and wet ingredients. Add the dry ingredients in three additions, alternating with the milk and sour cream. Begin and end with the dry ingredients. Mix until just combined, avoiding overmixing to ensure a tender crumb.

Step 6: Pour and bake. Pour the batter evenly into the prepared bundt pan. Tap the pan on the counter to release any air bubbles. Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.

Step 7: Cool the cake. Allow the cake to cool in the pan for 15 minutes. Then, carefully invert it onto a wire rack and let it cool completely before frosting.

Step 8: Make the chocolate frosting. In a medium bowl, beat the softened butter until creamy. Gradually add the powdered sugar and cocoa powder, mixing well after each addition. Add the heavy cream, vanilla extract, and a pinch of salt. Beat until the frosting is smooth and fluffy.

Step 9: Frost the cake. Spread the chocolate frosting evenly over the cooled cake using an offset spatula. Create decorative swirls for a visually appealing finish.