Preheat oven to 350F. Mist a 12-cup muffin tin and 4 cups of a 6-cup tin with gluten-free cooking spray.
In a bowl, whisk rice flour, almond meal, baking soda, salt and cinnamon.
Place chocolate and butter in a heatproof bowl; set over a pan of simmering water.
Let stand until chocolate and butter have melted, stirring often.
Remove from heat; whisk in cocoa.
In a large bowl, using an electric mixer, beat eggs and sugar on medium speed until smooth. Beat in vanilla. Slowly add chocolate mixture; beat on low for 1 minute. Beat in flour mixture.
Fill each muffin cup 2/3 full.
Bake until a toothpick stuck into middle of a brownie comes out clean, about 15 minutes.
Let cool in pans on a wire rack for 5 minutes, then remove to rack to cool completely.