Preheat oven to 350 F.
Line 8x8 pan with parchment paper.
Combine all crust ingredients until crumbs are fully moistened.
Press moistened crumbs into the bottom of the pan.
Heat Bailey's and butter over low heat until butter is melted and Bailey's is hot.
Put cocoa powder and oil in heat-proof mixing bowl.
Add heated mixture to mixing bowl and combine.
Mix in egg and yolk.
Stir in sugar.
Add in flour, salt, and espresso and mix until incorporated.
Stir in chips.
Pour batter over crust.
Bake for 25 minutes.
Turn oven up to broil.
Cover top of brownies with marshmallows.
Broil for 1-2 minutes till the marshmallows are just toasted. Watch closely, they will burn quickly!
Cool, cut, and enjoy!