Add the powdered sugar, milk, and vanilla to a small bowl. Use a wire whisk to stir until the glaze is smooth and whithout lumps.
Make the whipped cream:
Pour the heavy whipping cream into a medium mixing bowl. Add the confectioners' sugar and vanilla extract. Beat until fairly stiff. Scoop the whipped cream into a disposable piping bag fitted with a 1/2 inch star nozzle and store in the refrigerator until you're ready to use.
Make the pancake batter:
Whisk together the egg, milk, vanilla extract and butter in a large bowl.
Sift the dry ingredients (flour, sugar, baking powder, and salt) into the wet ingredients. Stir until well combined and no small lumps remain. Fold in the jimmies.
Cook the pancakes:
Preheat oven to 150 F and place a wire rack over a baking sheet in the oven.
Heat a large nonstick skillet over medium low heat. Coat it with nonstick cooking spray. You'll know the pan is hot enough when you flick a few droplets of water into it and it sizzles.
Pour a 1/3 cup of batter into the pan. Pour in 1 tbsp water, then cover the pan. Let cook for 2-3 minutes until small bubbles emerge throughout the pancake surface and the edges are set.
Flip the pancake. Cook for an additional 2-3 minutes until the pancake is golden brown.
Keep the pancake warm in the oven while you use the remaining batter to cook the 5 additional pancakes.
Assemble the pancake cake:
When you are done, you should have six roughly 6-inch pancakes. Stack them on a cake plate. Pour the glaze over the top, being sure to drip around the edges and down the sides. Pipe a rosette of whipped cream onto the top and sprinkle with the extra sprinkles