Orly's Passover Gluten Free Chocolate Nut Butter Brownies

These are adapted from the Orly the Baker gluten-free Peanut Butter Brownies sold at Chompies restaurants in Arizona. I usually make these brownies with a peanut butter frosting, but they are equally as delicious with almond or cashew butter.  You can find Kosher for Passover versions of all of the ingredients in this recipe.  If you can't find mini marshmallows, cut large ones into small chunks.  

Makes 9 large brownies or 16 small brownies

1 cup (250g) butter or margarine
1 cup (300g) tightly packed brown sugar
3 eggs
1 cup (250g) dark chocolate, melted
½ cup (80g) potato starch
½ tsp baking powder
½ cup (65g) cocoa powder
Pinch of salt
¾ heaping cup (100g) walnuts chopped
1 cup (100g) mini passover marshmallows  

Nut Butter Frosting (optional):
¼ (57g) cup butter or margarine
½ (125g) cup cashew or almond butter
1 cup (115g) powdered sugar
1 tbsp cream
1 tsp vanilla

Heat: Pre-heat oven to 350 degrees F.  Grease and line a 9" square tin with baking paper. 

Mix: In the bowl of a stand mixer with the paddle attachment, cream together the butter and brown sugar for about 3 minutes.  Add eggs, one at a time. Add the melted chocolate and mix until fully incorporated.   In a separate bowl, mix together potato starch, baking powder, salt, and cocoa powder.   Add the dry ingredients to the wet and mix on medium-high speed until combined into a thick batter.  Add walnuts (or pecans) and marshmallows (or chocolate chips) and incorporate through the mixture.  Pour the batter into the pan and use a spatula to spread it evenly.

Frosting: Cream the butter and nut butter together until combined.  Gradually add the powdered sugar and starting on slow speed, whip together until the sugar is completely mixed in.  Add 1 Tbsp of cream and 1 tsp of vanilla extract and continue to whip together on high speed until you have a soft and smooth consistency.  Spread this mixture on top of the brownie batter or swirl within the batter using an offset spatula. 

Bake: Bake brownies on center rack for 30-35 minutes.  Allow the brownies to cool on a rack and serve with vanilla ice cream!