Preheat oven to 350°F. Generously butter a 10-cup bundt pan and set aside.
In a microwave safe bowl, heat unsweetened chocolate at half power at 30 second intervals. Stir often. Heat until chocolate is melted. Set aside.
In a glass measuring cup, stir together instant espresso powder and cocoa powder. Add enough hot water until liquid mixture measures 1 cup. Stir until powders are dissolved. Add milk and let cool.
In the bowl of a stand mixer with a paddle attachment, cream butter and sugar until light and fluffy. Add eggs one at a time, making sure egg is incorporated before adding the next. Scrape down bowl as needed.
Add slightly cooled melted chocolate. Continue to mix on low-medium speed until combined.
In a medium bowl, whisk together flour, baking soda, and salt. With the mixer on low, add 1/3 of milk mixture, then 1/2 of flour mixture. Repeat, ending with the milk mixture. Mix until combined.
Peanut Butter Cake Filling:
In a medium bowl, cream together butter and peanut butter until smooth. Add sugar and mix until combined. Add half of the beaten egg. Discard other half of egg. Mix until combined.
Fold in flour and salt. Add milk and stir to combine. Mix until flour is incorporated.
Cake Assembly:
Add half of chocolate batter to prepared bundt pan. Distribute peanut butter cake filling on top of chocolate layer. Swirl with knife to spread out peanut butter batter. Add remaining chocolate batter to cover peanut butter batter.
Bake for 50-60 minutes, until toothpick inserted in cake comes out clean. Let cool in pan for a couple of minutes before unmolding. Let cool to room temperature of wire rack.
Chocolate Glaze:
Over a double boiled, melt together chocolate and butter until smooth. Alternatively, you can microwave it at half power at 30 second intervals until melted.
Remove from heat and whisk in glucose. Pour over cooled bundt cake.
Peanut Butter Glaze:
Stir together sifted powdered sugar, peanut butter, and salt. Add milk and stir until smooth. Add additional milk if glaze is too dry. If glaze is too thick, add additional sifted powdered sugar. Drizzle peanut butter glaze over chocolate glazed bundt cake.
Notes
The peanut butter cake filling is not creamy. It will be more cake-like in texture.