Preheat oven to 350F. Line an 8x8” baking dish with parchment paper and set aside.
Melt butter, chocolate chips, and maple syrup together in double boiler, whisking continuously until mixture is smooth. Set aside to cool.
In a large mixing bowl, beat together eggs, sugar, and extract on high speed for 2-3 minutes.
Next, while whisking, slowly pour all of the warm chocolate mixture in with the eggs, sugar and extract. Whisk in until well combined.
Add oat and almond flour to mixture and stir with a spatula just until combined.
Stir in 1 cup of marshmallow pieces then pour brownie mixture into prepared pan.
Bake in the oven for 45-55 minutes. Let cook and enjoy.