In a large bowl, combine the all-purpose flour, baking powder, baking soda, granulated sugar, and salt. Whisk these dry ingredients together until they are evenly mixed, ensuring that there are no lumps.

In another bowl, beat the egg until it is well mixed, then stir in the sourdough discard and milk until combined. Add the melted butter, mixing gently until everything is smoothly incorporated.

Pour the wet mixture into the bowl with the dry ingredients. Use a spatula to fold the ingredients together gently, being careful not to over-mix. A few small lumps are fine.

In a small bowl, create the cinnamon swirl by mixing the brown sugar, ground cinnamon, and melted butter. Set aside for later use.

Heat a non-stick skillet or griddle over medium heat until ready.

Pour about ¼ cup of pancake batter onto the griddle for each pancake, providing space for them to spread.

Place small spoonfuls of the cinnamon swirl mixture on each pancake while the batter is still uncooked. Use a toothpick or skewer to gently swirl the mixture into the batter.

Allow the pancakes to cook until bubbles form on the surface and the edges start to set, about 3 minutes.

Flip the pancakes and continue to cook for another 2 minutes, or until golden brown and cooked through.

While pancakes are cooking, whisk together powdered sugar, maple syrup, vanilla extract, and milk in a small bowl until smooth.

Stack the pancakes on plates and drizzle generously with the maple glaze. Serve warm.