In a large mixing bowl, whisk together the flour, sugar, baking powder, salt, and 1 teaspoon cinnamon until evenly combined. In a separate bowl or measuring jug, whisk the warm milk and egg until smooth, then stir in the melted butter. Pour the wet ingredients into the dry ingredients and mix until just combined; the batter should be slightly lumpy.
Add an extra teaspoon of cinnamon directly into the batter and gently swirl with a toothpick or skewer to create chaotic cinnamon streaks without fully blending it in, producing a marbled effect.
Preheat a non-stick skillet or griddle over medium heat until a few drops of water dance on the surface and evaporate quickly. Lightly grease if necessary.
Pour approximately ¼ cup of batter onto the hot skillet, observing the chaotic cinnamon streaks spread across the surface. Let cook until bubbles form on the top and the edges appear set, about 2-3 minutes.
Carefully flip the pancake using a spatula and cook for another 1-2 minutes until golden brown and cooked through, with visible cinnamon streaks swirling within the surface.
Repeat with remaining batter, adjusting heat as needed to prevent burning. Serve the stacks warm, showcasing their irregular edges and cinnamon swirls.
