Turtle Brownies

For brownie layer
3/4 cup plus 2 tablespoons all-purpose flour
1/4 teaspoon baking powder
1/2 teaspoon salt
4 oz semisweet chocolate, chopped
1 oz unsweetened chocolate, chopped
1 stick (1/2 cup) unsalted butter, cut into pieces
1 cup packed brown sugar
1 teaspoon vanilla
2 large eggs

For caramel-pecan layer
3/4 cup granulated sugar
1/3 cup light corn syrup
3 tablespoons water
1/3 cup heavy cream
1 teaspoon vanilla
1 1/2 cups pecans (6 oz)

Garnish: melted semisweet chocolate

Preheat oven to 350°F. Butter and flour a 9-inch square metal baking pan, knocking out excess flour.

Make brownie layer:

Whisk together flour, baking powder, and salt in a small bowl.
Melt chocolates and butter in a 2-quart heavy saucepan over low heat, stirring until smooth, then remove from heat. Cool to lukewarm, then stir in brown sugar and vanilla. Add eggs 1 at a time, beating with a wooden spoon after each addition until mixture is glossy and smooth. Add flour mixture and stir until just combined.
Spread batter evenly in baking pan and bake in middle of oven until a tester comes out clean, 30 to 35 minutes. Cool completely in pan on a rack.

Make caramel-pecan layer:

Bring sugar, corn syrup, water, and a pinch of salt to a boil in a 3-quart heavy saucepan over moderate heat, stirring until sugar is dissolved, then boil, without stirring, until mixture turns a golden caramel color, about 10 minutes. Remove from heat and carefully add cream and vanilla (mixture will bubble and steam). Stir in pecans and immediately pour over brownie layer, spreading evenly. Cool completely in pan on rack.

Prepare garnish:

Spoon chocolate into a small sealable plastic bag and seal, forcing out excess air. Squeeze chocolate into 1 corner, then cut a tiny slice off corner to form a small hole. Squeeze chocolate decoratively over brownies.
Chill brownies, loosely covered, until caramel and chocolate are firm, at least 4 hours.
Just before serving, cut chilled brownies into 64 (1-inch) squares and remove from pan while still cold, then bring to room temperature.