Grease a 9x13 pan with butter and line it with parchment paper. Preheat oven to 350.
Add the butter to a pan over high heat. Melt the butter and cook to brown. Remove from heat.
Pour the butter over the chocolate chips and stir to combine. Pull the espresso shots and add them to the mixture. Stir again. Let this sit while you get the other ingredients together, and stir it once in a while to continue letting the chocolate melt.
Add the eggs, sugar, and vanilla to one bowl. Add the flour, cocoa powder, and salt to another.
Use a hand mixer to beat the eggs and sugar together until light and fluffy. Pour in the cooled chocolate and butter mixture and continue to beat for 3 minutes.
Fold/stir in the flour mixture until fully combined.
Pour the brownie mix into the greased pan.
Add all the eggnog topping ingredients to a food processor. Process until smooth. Scrape down the sides and process another 15 seconds until fully combined.
Pour the eggnog mixture over the brownie mixture. Use a knife or spatula to make waves in the pan and marble the eggnog topping and brownie batter together.
Bake at 350 for about 45 minutes until just set and still slightly undercooked in the center.