**Prepare the Apple Filling:** In a small saucepan over medium heat, melt the butter. Add diced apples, sugar, cinnamon, and nutmeg, stirring to combine. Cook for 5–7 minutes until the apples soften. Stir in the cornstarch slurry and cook for another 1–2 minutes until the mixture thickens. Remove from heat and let cool slightly.
**Assemble the Taquitos:** Place a small amount of apple filling onto the lower third of a tortilla. Roll the tortilla tightly around the filling and secure with a toothpick if needed. Repeat with the remaining tortillas and filling.
**Preheat the Air Fryer:** Preheat your air fryer to 375°F (190°C) for 3 minutes.
**Brush and Coat:** Lightly brush each taquito with melted butter, then roll in cinnamon sugar until fully coated.
**Air Fry:** Place the taquitos seam side down in the air fryer basket, leaving space between each one. Air fry for 6–8 minutes, flipping halfway through, until golden brown and crispy.
**Serve:** Remove from the air fryer and let cool slightly. Serve with whipped cream, caramel sauce, or vanilla ice cream for dipping.