How to Make It
In a medium saucepan, whisk the cornmeal into the cold water and bring to a boil, whisking. Simmer over moderate heat until thickened to a porridge, 4 to 5 minutes. Transfer the mixture to a large bowl and whisk in the buttermilk and the egg yolk.
In another bowl, whisk the all-purpose and rice flours with the sugar, baking powder and baking soda. Whisk the dry ingredients into the cornmeal mixture. In a large bowl, using a handheld mixer, beat the 2 egg whites with the salt at high speed until firm peaks form. Gently fold the beaten egg whites into the batter.
Heat a large griddle. Brush the hot griddle with butter and ladle a scant 1/4 cup of batter onto the surface for each pancake, allowing a little space between them. Cook the pancakes over moderate heat until bubbles appear on the surface, about 2 minutes. Flip the pancakes and cook until risen and browned on the bottom, about 2 minutes longer. Serve the pancakes immediately with the Lemon-Sage Brown Butter and maple syrup. Repeat with the remaining batter.