Preheat oven to 350°F. Line a 13x9-inch baking pan with heavy-duty foil, letting excess extend over sides of pan. Spray with baking spray with flour.
For crust: In the work bowl of a food processor, combine flour, butter, confectioners’ sugar, and salt. Pulse until mixture is crumbly, 12 to 14 times. Reserve ⅓ cup crumb mixture. Press remaining crumb mixture into bottom of prepared pan.
Bake until lightly browned, about 14 minutes. Let cool for 20 minutes.
For brownie: In a large bowl, whisk together sugar, flour, cocoa, baking powder, and salt. Add melted butter, eggs, and vanilla, stirring until smooth. Stir in chopped chocolate. Spread over prepared crust.
Bake until firm to the touch, 25 to 30 minutes. Let cool for 30 minutes.
For caramel: In a large heavy saucepan, place sugar. In a small bowl, stir together 9 tablespoons water and corn syrup. Pour over sugar, swirling to coat. Cook over medium-high heat, without stirring, until mixture is amber brown, 10 to 14 minutes. Remove from heat. Add butter, stirring until melted (mixture will foam). In a microwave-safe bowl, heat cream over high heat until hot but not boiling, about 40 seconds. Slowly add hot cream, vanilla, and salt to sugar mixture, stirring until smooth. Let cool slightly. Reserve ½ cup caramel. Pour remaining caramel over brownie.
For topping: Sprinkle brownies with chocolate, pecans, and reserved ⅓ cup crumb mixture.
Bake for 5 minutes. (The crumb topping will not be browned.) Let cool completely at room temperature overnight (do not refrigerate—the chocolate will bloom). Using excess foil as handles, remove from pan, and cut into bars. Just before serving, drizzle with reserved ½ cup caramel.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/turtle-bars/