Begin by preheating your oven to 350°F (175°C). Prepare a 9-inch round cake pan by greasing and lightly flouring it or opt for convenience by lining the bottom with parchment paper.
In a large mixing bowl, thoroughly whisk together the all-purpose flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, blend together the melted unsalted butter, eggs, vanilla extract, and buttermilk until the mixture is smooth and creamy.
Pour the wet mixture into the bowl containing the dry ingredients. Stir gently until just combined, being mindful not to overmix.
Carefully fold in the semi-sweet chocolate chips and dark chocolate chunks.
Transfer the cake batter into the prepared pan, smoothing the top with a spatula.
Place the pan in the preheated oven and bake for 30-35 minutes.
After baking, remove the cake from the oven and let it cool in the pan for about 10 minutes. Then, carefully transfer the cake to a wire rack to cool completely.
Once the cake has cooled, sprinkle the top generously with milk chocolate shavings.
Slice the cake into generous portions and serve on its own, or with whipped cream or ice cream.
Notes
For a homemade buttermilk, mix milk with lemon juice and let it sit for a few minutes.