In a large bowl or the bowl of a stand mixer, cream together butter and sugar for 3-5 minutes or until light and fluffy.
Add eggs one at a time, followed by vanilla, mixing until incorporated after each addition.
Mix in sour cream until well combined.
Sift in flour, cocoa powder, espresso powder, baking powder, and baking soda. Fold in with a rubber spatula. Mixture should be fully combined, but do not overmix.
Carefully pour in boiling water and gently mix to combine (don't splash any onto yourself!). Mix only until the batter is fully combined.
Spray a 10-12 inch fluted tube or Bundt pan with baking spray, including all crevices. Pour batter into prepared pan. Carefully drop once or twice from an inch or two onto the counter to elmininate air bubbles.
Bake in preheated oven for 60-70 minutes, or until a toothpick entered into the center of the cake comes out clean. Cool 10 minutes in the pan, then turn out on to a wire rack to cool completely.
Chocolate Ganache Glaze
Heat chopped chocolate and heavy cream in microwave for 20-second intervals until beginning to melt.
Stir to finish melting until smooth.
Add corn syrup and stir until glossy.
If desired, allow to cool in the fridge for 15 minutes for a slightly thicker consistency.
Pour glaze over cooled cake, allow to set, and serve.
Freezing: This cake freezes well for up to two months! Once the glaze has cooled and set completely, you can freeze the cake whole or in slices (I recommend slices so that you can thaw them individually for a single-serving treat anytime!). Just freeze the cake or the slices uncovered for about 30 minutes to solidify the glaze, then wrap in plastic wrap and then in heavy-duty aluminum foil and freeze. When you are ready to eat your chocolate sour cream pound cake, just thaw the wrapped cake or wrapped slices on the countertop, and enjoy!