Preheat the oven to 400°F (200°C). Lightly grease a nonstick baking sheet or line it with parchment paper.
In a medium mixing bowl, whisk together the flour, baking powder, kosher salt, and ground cinnamon until evenly combined.
In a separate large bowl, whisk the melted butter and granulated sugar together.
Add the egg, vanilla, and unsweetened applesauce. Whisk until the mixture is smooth.
Gradually add the dry ingredients to the wet ingredients. Fold everything together just until combined. Avoid overmixing.
Gently fold the finely diced apples into the batter until evenly distributed.
Scoop tablespoon-sized portions of batter onto the prepared baking sheet, leaving a little space between each one.
Bake the Apple Fritter Bites for approximately 10 minutes, or until the bites are set and beginning to turn golden.
Turn on the broiler and broil briefly, approximately 1–3 minutes, watching continuously. Remove the fritter bites as soon as the tops become more deeply golden and lightly caramelized. Broilers vary considerably, so do not leave them unattended.
Meanwhile, prepare the apple cider glaze. Place the powdered sugar in a medium bowl and gradually whisk in the apple cider or juice until smooth. Start with less liquid and add more as needed to achieve a thick but brushable glaze.
Brush or spoon the glaze generously over the warm fritter bites.
Let the glaze set slightly before serving. Enjoy warm or at room temperature.