Place buckwheat flour, brown rice flour, corn starch, baking powder, and salt in a large bowl. Whisk to get it well combined.
In another bowl, beat egg for about 1 minute. Pour in coconut milk and canola oil. Pour this mixture into flour mixture. Stir to get ingredients well mixed and a smooth batter forms.
Pour ½ cup batter onto a pre-heated waffle iron and cook until golden brown, about 3 to 4 minutes.
Serve immediately with butter, maple syrup, or jam.