Make the pound cake: Preheat the oven to 350˚. Butter the bottom and sides of a 9-by-5-inch loaf pan, then line with parchment paper in two overlapping strips, leaving an overhang. Butter the parchment and lightly dust with flour, tapping out the excess.
Microwave the heavy cream in a small microwave-safe bowl until steaming, about 1 minute. Pour over the cocoa powder in a medium bowl and stir to make a thick smooth paste; let cool.
Whisk the eggs, egg yolk and vanilla in a medium bowl until frothy; set aside. Beat the butter and cane sugar in a large bowl with a mixer on medium speed until well combined, 1 to 2 minutes. Scrape down the bowl and increase the mixer speed to medium high. Beat until pale and fluffy, 6 to 7 minutes.
Add the cocoa mixture to the butter mixture; beat until well combined, 1 minute. Reduce the mixer speed to low and beat in the flour until just combined. Gradually add the egg mixture and beat until combined. Scrape down the bowl, increase the speed to medium and beat until smooth and fluffy, about 30 seconds. Stir in the mini chocolate chips.
Transfer the batter to the prepared pan and smooth the top. Bake until the top springs back when gently pressed and a toothpick inserted into the center comes out clean, 1 hour 10 minutes to 1 hour 20 minutes. Transfer to a rack and let cool 10 to 15 minutes in the pan. Lift the cake from the pan and remove the parchment; return the cake to the rack to cool completely. Dust with confectioners' sugar just before serving.
Quality ingredients make a big difference in pound cake. Try using premium butter — and if you can, use organic cane sugar. It gives the loaves a great crunchy top.