Whisk egg and yogurt together in a large bowl. If using a thin yogurt, do not add any milk. If using a regular yogurt, add 2 tablespoons milk. If using a thick, Greek-style yogurt, add 3 to 4 tablespoons milk. Use a flavored yogurt, to achieve different flavors. I have also done a key lime pie flavored pancake using key lime pie yogurt, ¼ cup plus a dash of lime juice (adding no milk) and adding about ½ tsp lime zest. It was a more subtle flavor than I had hoped for but it was still delicious.
Whisk in melted butter and vanilla extract. In a separate, small bowl, combine flours, sugar, baking powder and salt. Stir dry ingredients into wet only until dry ingredients are moistened. A few remaining lumps is fine.
Melt a pat of butter in the bottom of a skillet over medium heat. Scoop slightly less than ¼ cup batter into your skillet leaving room between pancakes. The batter is thick, so gently flatten the pancake using a spatula or I use my ¼ cup measuring cup that I use to scoop the batter out to flatten them. Cook for 3 to 4 minutes until the pancakes are dry around the edges and bubbles form on top. Flip and cook for about 3 more minutes. If the pancakes are cooking too quickly, lower the heat because if they cook too fast the center will be under cooked since the pancakes are on the thicker side. Keep the pancakes in a warm oven as they are done cooking, until you are ready to eat.
Note: These are perfect to make in large batches and freeze. I place wax paper in between the pancakes and freeze them in a ziploc bag.