1. Prepare the pan

Preheat the oven to 350°F (180°C). Thoroughly grease a 10-cup Bundt pan, including the center tube and decorative ridges. Lightly flour the pan if recommended.

2. Cream the butter and sugar

In a large mixing bowl, beat 200 g softened unsalted butter with 200 g granulated sugar until pale, light, and fluffy.

3. Add the eggs and vanilla

Beat in 4 large eggs, one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.

4. Finish the vanilla batter

In a separate bowl, whisk together 250 g all-purpose flour and 2 teaspoons baking powder. Gradually add the dry ingredients to the butter mixture, alternating with 100 ml milk. Mix just until combined.

5. Prepare the chocolate-cinnamon batter

Divide the batter evenly between two bowls. Leave one portion plain. Stir 2 tablespoons unsweetened cocoa powder, 2 tablespoons granulated sugar, and 2 tablespoons ground cinnamon into the second portion until evenly combined.

6. Create the marble pattern

Spoon alternating portions of vanilla and chocolate-cinnamon batter into the prepared Bundt pan. Gently swirl a butter knife or skewer through the batter a few times to create a marble effect without completely blending the colors.

7. Bake the cake

Bake for 45–55 minutes, checking at 45 minutes. Insert a toothpick into the thickest part of the cake, away from the center tube. It should come out with a few moist crumbs and no wet batter.

8. Cool the cake

Let the cake rest in the pan for approximately 10 minutes. Carefully invert it onto a wire rack and allow it to cool completely.

9. Prepare the chocolate glaze

Place 100 g chopped milk chocolate in a microwave-safe bowl. Microwave in short intervals, stirring between each, until completely melted and smooth.

10. Glaze and serve

Drizzle the melted chocolate over the cooled Bundt cake. Allow the chocolate to set slightly before slicing and serving.