Separate the eggs into two medium bowls, one with the yolks and one with the whites. Lightly beat the egg yolks and add the sourdough starter, milk, yogurt (if using), and molasses. Stir well.
In a separate medium bowl, combine the soft-wheat pastry flour, buckwheat flour, sugar, baking soda, baking powder, and salt. Add the sourdough starter mixture and stir until no dry streaks remain. Stir in the melted butter until just combined. Let the batter rest for 15 to 30 minutes.
For the lightest pancakes, whisk the egg whites to stiff peaks. Alternatively, if you prefer, you can skip this step. Carefully fold the egg whites into the batter until just combined.
Heat a griddle or skillet over medium heat. Add a small pat of butter or oil and let it melt. Pour about ¼ cup of the batter onto the griddle for each pancake. Cook until bubbles start to form and remain open, and the edges of the pancakes start to darken, about 3 to 4 minutes. Flip the pancakes and cook until well-colored on the bottom, about 4 more minutes.
Serve the pancakes warm, topped with butter, and a drizzle of maple syrup. You can also crumble some walnuts/pecans or gingersnaps over top.