To make the cinnamon filling, in a bowl, still together the granulated sugar, flour, cinnamon and salt. Add the butter and, using the back of a spoon, mash the butter into the flour mixture until all of it is absorbed into the butter, forming a paste. Set the cinnamon filling aside.

To make the cream cheese frosting, in the bowl of an electric mixer fitted with the flat beater, beat together the cream cheese and butter on medium speed until light and fluffy, 2 to 3 minutes. Add the confectioners' sugar, reduce the speed to low and beat until combined, 1 to 2 minutes, stopping the mixer occasionally to scrape down the sides of the bowl. Add 3 Tbs. of the milk and beat until combined, about 1 minute. The frosting should be thick but still pourable; add more milk if needed to thin it. Transfer the frosting to a small bowl; set aside.

To make the pancakes, in a bowl, whisk together the flour, baking powder, salt and granulated sugar. In another bowl, lightly whisk the egg yolks, then whisk in the milk and the 4 Tbs. melted butter. Whisk the egg yolk mixture into the flour mixture until well combined; the batter will be lumpy. Using an electric mixer fitted with the whisk attachment, beat the egg whites on high speed until stiff but not dry peaks form, 2 to 3 minutes. Using a rubber spatula, gently fold the whites into the batter in two additions.

Put 1/8 tsp. melted butter in each well of a filled-pancake pan. Set over medium heat and heat until the butter begins to bubble. Pour 1 Tbs. batter into each well. Spoon 1/2 tsp. of the cinnamon filling into the center of each pancake and top with 1 Tbs. batter. Cook until the bottoms are golden brown and crispy, about 3 minutes. Using 2 skewers, flip the pancakes over and cook until golden and crispy, about 3 minutes more. Transfer the pancakes to a plate. Repeat with the remaining batter and filling.

Drizzle the pancakes with the frosting and serve immediately.