Gather all ingredients and equipment, then carefully separate eggs — whites into one clean, dry bowl and yolks into another. Ensure bowls and beaters are completely grease-free so the whites whip properly.
Add the Kodiak Cakes mix, baking soda, and brown sugar (if using) to a large mixing bowl and whisk to combine, breaking up any lumps.
In a separate bowl, whisk together the buttermilk, egg yolks, vanilla extract, and melted butter until smooth and fully incorporated.
Pour the wet ingredients into the dry and gently mix until just combined — a few lumps are fine. Let the batter rest 5 minutes to fully hydrate the mix.
Using an electric mixer, beat egg whites on medium then high speed for 2–3 minutes until stiff, glossy peaks form that stand straight up when beaters are lifted.
Add egg whites to the batter in three additions, gently folding with a rubber spatula using a cutting-and-turning motion until no white streaks remain — do not overmix.
Heat a non-stick griddle or skillet over medium heat (350–375°F / 175–190°C), then lightly grease with butter or cooking spray, wiping away any excess.
Pour ¼ cup batter per pancake onto the griddle without spreading. Cook 2–3 minutes until bubbles form across the surface and edges appear set and slightly dry.
Flip each pancake once with a thin spatula and cook the second side 1–2 minutes until golden brown. The center should spring back slightly when gently pressed.
Transfer cooked pancakes to a plate covered loosely with foil, or keep warm in a 200°F (95°C) oven. Continue cooking remaining batter, re-greasing the griddle between batches.