Cut the apples into quarters and remove the cores. Slice each quarter lengthwise into very thin wedges, approximately ⅛-inch thick (I am usually able to get 40-50 thin slices out of a large apple). Pat the apple slices dry and set aside. Heat a lightly greased nonstick skillet over medium-low heat.
In a medium bowl, whisk together the flour, baking powder, cinnamon, and salt until combined.
In a separate large bowl, whisk together the egg, milk, maple syrup, and vanilla extract. Slowly pour in the melted, slightly cooled butter while whisking until combined.
Pour the dry ingredients into the wet ingredients and gently mix until just combined. A few small lumps are fine, but be careful not to overmix. The batter should be thin enough to coat the apples without clinging too thickly.
Dip the apple slices in batches into the pancake batter, making sure they are fully coated on both sides. Lift the apple slices one by one and let any excess batter drip off for a few seconds.
Place the coated apple slices onto the preheated skillet, leaving a little space between each one. Cook for approximately 2–3 minutes per side, until golden brown and the pancake coating is cooked through. Repeat with the remaining apple slices.
As the apple pancake dippers are cooking, mix together the granulated sugar and cinnamon in a shallow bowl. While the apple pancakes are still warm, immediately toss them in the cinnamon sugar mixture until evenly coated. If needed, brush the pancake dippers with a little melted butter to help the coating stick.