Preheat the oven to 325°F. Grease a regular bundt pan with softened butter or nonstick spray, then dust the inside evenly with cocoa powder using a sifter; tap out any excess.

In a small heatproof bowl, dissolve 2 teaspoons instant coffee powder in 2 tablespoons hot water. Set the bowl aside to cool to room temperature.

In a large mixing bowl, beat 1 cup softened unsalted butter and 2 cups granulated sugar with a hand or stand mixer on medium-high until light and airy, about 4 minutes.

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

In a separate large bowl, whisk together 2 cups all-purpose flour, 1/2 cup cocoa powder, 1/2 teaspoon baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon salt until evenly combined and no white streaks of flour remain.

Add the dry ingredients to the butter mixture in three parts, alternating with the 1 cup sour cream (room temperature): add one-third of the dry ingredients and mix until mostly combined, add half of the sour cream and mix until just combined, repeat (dry, then sour cream) and finish by adding the last third of the dry ingredients. Mix only until combined at each addition—do not overmix.

Stir in the cooled coffee mixture until just combined. Fold in the 1/2 cup mini semi-sweet chocolate chips, reserving a small handful if you want to sprinkle some on top before baking.

Pour the batter into the prepared bundt pan and smooth the top. If you reserved chips, sprinkle them evenly over the top of the batter.

Bake for 60–70 minutes, or until a toothpick inserted into the cake center comes out clean or with a few moist crumbs. Remove from the oven and let the cake cool in the pan on a wire rack for 15 minutes.

After 15 minutes, invert the cake onto the wire rack and let it cool completely before glazing.

To make the glaze, sift together 1 cup powdered sugar and 3 tablespoons unsweetened cocoa powder into a bowl. Stir in 1/2 teaspoon vanilla extract. Gradually add 3–4 tablespoons milk, a little at a time, stirring until the glaze reaches a pourable consistency.

When the cake is completely cool, pour the glaze over the top, letting it drip down the sides. Immediately sprinkle 1/4 cup chocolate shavings over the glaze.

Slice and serve.