In a medium pitcher/glass measuring cup, whisk together the eggs, sour cream and heavy cream. Mix in the espresso and vanilla mixture. Set aside.
1 cup sour cream, 1/8 cup heavy cream, 5 eggs
In the large bowl of your mixer, sift together the flour, cake flour, cocoa, baking powder, and salt. Add the sugar and brown sugar, stir to combine.
2 cup all-purpose flour, 1/2 cup cake flour, 1 cup cocoa powder, 2 teaspoon baking powder, 1 teaspoon salt, 1 1/3 cup granulated sugar, 1 1/3 cup brown sugar
Cut the butter into small chunks and add to the dry ingredient mixture in your mixing bowl. Mix on low speed until the mixture resembles wet sand or coarse crumbs
1 cup butter
With the mixer on low, gradually add in half of the liquid mixture. Increase the speed to medium and beat for about 1 minute to fully combine and build some structure. Scrape down the bowl as necessary to ensure there are no unmixed ingredients.
Reduce the mixer to low again, gradually add in the remainder of the liquid ingredients. Increase to medium speed and beat for another minute.
Remove the bowl from the mixer and fold in the chocolate pieces with a spatula until evenly distributed.
1 1/2 cup chocolate chips
Spoon the batter into the prepared pan and smooth out the top.
Bake the cake on the middle rack of your oven for about 70 minutes or more, until a toothpick inserted comes out with a few moist crumbs and the cake starts to pull away just slightly from the sides of the pan.
Cool the cake in the pan on a rack for 10 to 15 minutes. Invert the cake onto another cooling rack, remove the pan and the parchment paper. Then invert the cake again so it is right side up. Allow the cake to completely cool on the rack.
Make the glaze
Place the chocolate in a medium heat safe bowl.
4 1/2 oz bittersweet chocolate
In a small sauce pan, heat the heavy cream, corn syrup, butter and salt just to a simmer. Immediately pour over the chocolate and let sit for about 1 minute.
1/2 cup heavy cream, 2 tbsp corn syrup, 1 tbsp butter, 1 pinch salt
Starting in the center of the bowl, stir the chocolate and cream mixture in widening circles until the mixture is fully combined, smooth and silky. Allow the glaze to sit at room temperature until desired thickness. If your cake is chilled, it is best to pour immediately as the cold cake will cause the glaze to set quickly. If your cake is room temperature, allow the glaze to cool until it falls in ribbon - or slightly longer if you prefer a thicker glaze.
Put a sheet of wax paper under the cooling rack the cake is on. Slowly pour the glaze around the top of the cake allowing it to drip naturally down the side. If you'd like to garnish with additional chocolate chips, let the glaze set up for a few minutes before sprinkling the chips on top.
micro chocolate chips
Notes
If your pan is a little too small, make sure you only fill it 2/3 full. Any leftover batter can be baked separately as a small loaf or cupcakes.