Preheat oven to 350°F and line a 9x13-inch baking pan with parchment paper.
In a large bowl, mix melted butter, granulated sugar, brown sugar, and vanilla until combined.
Add flour, baking powder, and salt to form a crumbly dough.
Press two-thirds of the dough into the prepared pan to form the crust.
In another bowl, toss apples with cinnamon, nutmeg, and lemon juice.
Spread apple mixture evenly over the crust.
Crumble remaining dough over the apples to create a topping.
Bake for 45–50 minutes, until golden brown and apples are tender.
Cool completely before cutting into bars.