Preheat your oven to 350°F (175°C). Thoroughly grease and flour a 10-cup bundt pan, making sure to get into all the crevices. In a medium heatproof bowl, combine the cocoa powder, chopped bittersweet chocolate, and espresso powder. Pour the hot water over the top, cover, and let it sit for 5 minutes.
Whisk the chocolate mixture until it is completely smooth and no lumps remain. Let it cool to room temperature, then whisk in the sour cream until fully combined.
In a separate small bowl, whisk together the all-purpose flour, baking soda, and salt.
In the bowl of a stand mixer with the paddle attachment, or in a large bowl with a hand mixer, beat the room temperature butter, brown sugar, and vanilla extract on medium-high speed until light and fluffy, about 4 minutes.
Reduce the mixer speed to low and add the eggs one at a time, mixing until just combined after each addition. Scrape down the sides of the bowl as needed.
With the mixer on low speed, add the flour mixture in three parts, alternating with the chocolate mixture in two parts, beginning and ending with the flour. Mix only until the last streaks of flour disappear. Do not overmix.
Pour the batter evenly into the prepared bundt pan. Bake for 45-55 minutes, or until a wooden skewer inserted into the center of the cake comes out with a few moist crumbs attached.
Let the cake cool in the pan on a wire rack for 10 minutes. Then, carefully invert the cake onto the rack to cool completely, at least 1 hour.
To make the glaze, place the chopped semisweet chocolate in a small bowl. In a small saucepan, heat the heavy cream and corn syrup over medium heat until it just begins to simmer. Pour the hot cream over the chocolate and let it sit for 2-3 minutes, then whisk until smooth. Stir in the peppermint extract. Let the glaze cool and thicken for about 10 minutes before drizzling it over the cooled cake. Sprinkle with crushed candy canes before the glaze sets.