Preheat oven to 325°F (170°C).

For cake: In a large bowl, whisk together melted butter and sugars. Whisk in eggs, cider, and vanilla until well combined.

In a medium bowl, whisk together flour, baking powder, cinnamon, salt, and nutmeg.

Using the large holes of a box grater, shred apples.

Whisk half of flour mixture into butter mixture until just combined. Fold in apples and any juices. Fold in remaining flour mixture just until no dry streaks remain.

In another medium bowl, stir together one-third of batter (about 2 cups or 500 grams) and dulce de leche; fold in pecans.

Spray a 10-cup Bundt pan with baking spray with flour.

Using a 1½-tablespoon spring-loaded scoop, scoop batters in an alternating pattern into prepared pan. Firmly tap pan on a kitchen towel-lined counter 7 to 10 times to settle batter and release any air bubbles.

Bake until a wooden pick inserted near center comes out clean and an instant-read thermometer inserted near center registers 205°F (96°C), 1 hour and 15 minutes to 1 hour and 25 minutes. Let cool in pan for 10 minutes. Invert cake onto a wire rack, and let cool completely.

For glaze: In a medium microwave-safe bowl, heat dulce de leche, 1 tablespoon (15 grams) water, vanilla, and salt on high in 10-second intervals, stirring between each, until warm and fluid; spoon onto cooled cake. Garnish with pecans, if desired. Store in an airtight container for up to 3 days.