Preheat oven to 375°. Line the bottom and two sides an 8-inch square pan with parchment paper, leaving a 1-inch overhang on the side or the pan. Spray with cooking spray.
Combine sweet rice flour, sugar, cocoa powder, and baking soda in a large bowl. In another bowl combine coconut milk, evaporated milk, eggs, vanilla and coconut oil. Add liquid mixture to flour mixture and stir until well-combined.
Pour batter into prepared pan. Bake at 375° for 1 hour or until cake is done when tested with a pick and sides are beginning to harden a bit. (over-baking is preferable to under-baking with this cake. under-baking produces an excessively gummy cake.) Allow cake to cool completely.
Cut cake into 16 (2-inch) squares. Dip squares, one at a time, into melted chocolate. Using a fork to carefully lift squares out of chocolate, gently shake off any excess chocolate and place squares on a wax paper-lined baking sheet. Chill for 20 minutes or until chocolate is set.