Preheat the oven to 350°F (175°C).

Grease and flour a 9x13-inch baking pan.

Combine the flour, baking powder, cinnamon, nutmeg, baking soda, and salt in a small bowl. Whisk to combine.

Combine the brown sugar, granulated sugar, and butter in a mixer bowl. Beat well until light and fluffy.

Mix in the eggs and vanilla, starting slowly, and then increase the speed for 30 seconds to fully incorporate.

Slowly stir in half of the flour mixture along with the milk. Mix until combined and then add the remaining flour mixture and milk until a smooth batter has formed.

Fold in the apples.

Transfer the batter to the prepared pan and spread into an even layer.

Bake for 35-40 minutes or until the toothpick test returns clean.

Cool the cake on a wire rack in the pan.

Melt the butter in a small saucepan over medium heat.

Whisk in the brown sugar and heavy cream. Bring to a boil and hold at a boil for 2 minutes - stirring constantly.

Remove from the heat and carefully stir in the vanilla and salt.

Pour the warm glaze over the cooled cake. Spread it evenly over the top and let set before serving.