Preheat oven to 350 degrees F. Spray and line a 9-inch nonstick cake pan with a round of parchment paper at the bottom. Melt butter. Put the quinoa, milk, eggs, melted butter, and vanilla into the bowl of a food processor fitted with the metal blade. Pulse to combine and then process until smooth, this will only take about 30 seconds or so. Add the sugar, 1/2 cup of the cocoa powder, baking powder, soda, and salt to the bowl and pulse to combine well. Turn into the prepared pan and bake for about 40-42 minutes until a toothpick comes out without wet batter sticking to it. Remember that if your pan has different dimensions, your cooking time will vary. Let the cake cool on a rack for about 15 minutes before turning out of the pan. Be careful when you flip the cake over as it will be delicate. I like to place a plate over the pan and then gently flip both over together. When the cake is completely cool, frost. To make the frosting whip the cream until it is starting to thicken, then add the sifted confectioners (powdered) sugar and remaining 2 Tbsp of the cocoa powder. Continue beating until thick and spreadable. Dont over beat!