In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, and salt.
In another bowl, whisk the egg, milk, melted butter, and vanilla extract until combined.
Pour the wet ingredients into the dry ingredients and mix until just combined. Do not overmix.
Heat a nonstick skillet over medium-low heat and lightly grease with butter or oil.
Spoon 1-2 tablespoons of batter into the skillet, place a chocolate square in the center, and cover with another spoonful of batter.
Cook for about 2–3 minutes or until bubbles form on the surface. Flip and cook for another 1–2 minutes until cooked through.
In a shallow bowl, mix 1/4 cup sugar and cinnamon. Coat the hot pancakes in the cinnamon-sugar mixture.
Serve warm and enjoy!