For the cookie layer:
1 1/2 cups (6 3/8 ounces) all-purpose flour
1 teaspoon baking powder
1/2 teaspoon kosher salt
8 tablespoons (1 stick; 4 ounces) room-temperature unsalted butter, cubed
1 cup (7 1/2 ounces) packed light or dark brown sugar
1 large egg
1 tablespoon vanilla extract

For the caramel-peanut layer:
4 tablespoons (1/2 stick; 2 ounces) unsalted butter
1/2 cup (5 1/2 ounces) light corn syrup
1/4 cup (1 7/8 ounces) packed dark brown sugar
1/4 cup (1 3/4 ounces) granulated sugar
1/4 cup heavy cream
1 cup (5 ounces) roasted salted peanuts

For the topping:
1 cup milk chocolate chips
Maldon salt or other flaky sea salt (optional)