Preheat the oven to 350°F and then grease or line a muffin tin for 12 muffins.In a small measuring cup, combine the flax with the water and set aside to thicken. Then combine the brown rice flour, cornmeal, salt, baking soda and baking powder in a large bowl and sift together.In a separate large bowl, combine the almond milk with the apple cider vinegar and stir together. Allow to sit for a few minutes.Next add the agave, melted butter and flax egg to the bowl with the almond milk and stir together. Add the frozen corn kernels and the dry ingredients and fold everything together until well combined.Fill each muffin tin 3/4 of the way full, or until all of the batter is used. Transfer to the oven and bake for 22-25 minutes, until light golden brown. You should be able to stick a toothpick in the center and have it come out clean.Allow to cool for at least 15 minutes before serving. Store in an airtight container in the refrigerator for up to 3 days.