Preheat the oven to 350 degrees. Mix the first 4 ingredients in a bowl and then mold into pie pan and up the sides. Bake for 15 minutes.
Start mixing the brownie ingredients. My gluten free mix is in the link above. Or use your favorite mix. add all dry ingredients and then add butter, eggs and vanilla extract. Bake for 20 minutes.
When done, refrigerate or freeze until cool.
Start marshmallow layer. Take 2 oz of water and put in a bowl and sprinkle gelatin on top, let thicken. In heavy saucepan mix remaining water, sugar and cream of tartar. Use a candy thermometer and cook and stir until heat reaches 238 degrees. Add gelatin to stand mixer.
Remove the pan from the heat and pour along the side into the stand mixer with a whisk attachment. Add salt and vanilla. This takes about 5 minutes and you will need to mix until it is thick and sticks to the whisk when lifted not runny. It should be shiny also.
Spread on the brownie layer. Place in refrigerator 2 - 3 hours until firm. Then heat the chocolate in the microwave at 30 second intervals at 70 percent. Spread a thin layer on top of marshmallow. My suggestion is a THIN layer. This is a very rich dessert.
Notes
If you aren't gluten-free then just make this with all your usual ingredients.