Preheat the oven to 350° F
Line an 8" square baking pan (see note) with two pieces of parchment paper, long enough to overlap on all four sides. Lightly oil the foil.
In a medium bowl, whisk together the almond flour, brown rice flour, cocoa powder, cinnamon, baking soda, and sea salt
Put half of the chocolate in a heatproof bowl and set the bowl over a saucepan of simmering water. Heat, stirring often, just until the chocolate is melted and smooth.
Remove from the heat and whisk in the olive oil.
Crack the eggs into a large bowl and whisk until frothy. Slowly add the maple syrup and maple sugar, whisking all the while, and continue whisking until the mixture is smooth.
Add the vanilla extract, then gradually add the chocolate mixture, whisking vigorously all the while.
Continue whisking until smooth and glossy.
Add the flour mixture and beat for about 1 minute.
Stir in the remaining chocolate and the walnuts.
Scrape the mixture into the prepared pan and smooth the top with a spatula.
Bake for 30 minutes or until a toothpick inserted in the center comes out clean.
Let cool to room temperature in the pan, then cover and refrigerate for at least 1 hour before cutting them