In a large bowl, whisk together the tahini, eggs, coconut oil, sugar and vanilla extract until smooth.
Pour in the almond flour, coconut flour, baking soda and salt, and mix together with a spatula. Fold in the chocolate and the marshmallows, reserving some of each to top.
Once evenly mixed, flatten into a parchment lined baking dish- mine was about 7u0022 x 10u0022. Press the extra chocolate and marshmallow pieces into the top of the batter.
Bake for 18 minutes for an under-baked texture, and 20-25 minutes for less gooey.
Let cool completely before slicing. Top with flakey sea salt if desired.