Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or an 8-inch round cake pan and line the bottom with parchment paper to ensure the cake releases easily.

In a medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking powder, and salt. Ensure there are no lumps in the cocoa powder for a completely smooth batter.

In a large mixing bowl, use an electric mixer to beat the softened butter and granulated sugar together until light, pale, and fluffy, which should take about 3 to 4 minutes. Add the eggs one at a time, beating well after each addition until fully incorporated.

Gradually alternate adding the dry flour mixture and the whole milk to the butter mixture, starting and ending with the dry ingredients. Mix on low speed just until combined, being careful not to overmix the batter.

Gently fold in the 1 cup of chopped toasted walnuts using a rubber spatula until they are evenly distributed. Pour the thick batter into the prepared baking pan, smoothing the top into an even layer.

Bake in the preheated oven for 45 to 55 minutes, or until a wooden toothpick inserted into the center of the cake comes out clean with just a few moist crumbs. Let the cake cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

While the cake cools, prepare the glaze by heating the dark chocolate chips and heavy cream in a microwave-safe bowl in 20-second intervals, stirring in between until melted and perfectly smooth.

Pour the warm chocolate glaze over the cooled cake, allowing it to drip down the sides. Sprinkle the remaining 1/4 cup of chopped walnuts on top, and let the glaze set for 15 minutes before slicing and serving.