Line a standard 8" square baking pan with foil.
For the crust, combine the 11/2 cup unsalted butter, 1 cup all-purpose flour, and 2 Tablespoons granulated sugar until sand-like in texture. Press evenly into the bottom of the prepared pan.
Bake at 350°F for 10 minutes. Remove from oven and make the turtle layer.
For the turtle layer, combine the 1/3 cup unsalted butter and 1/3 cup light brown sugar, in a small saucepan over medium heat. Bring to a boil and boil 1 minute, whisking to prevent burning.
Remove from heat and stir in 1/4 teaspoon vanilla extract; pour mixture over partially baked crust.
Sprinkle c1/3 cup pecans, chopped evenly over the caramel layer; return to oven and bake an additional 12-14 minutes, or until the edges are golden brown (caramel mixture will continue to bubble up while baking).
Remove from oven and immediately sprinkle with the 2/3 cup semi-sweet or milk chocolate chips,. Cool pan on wire rack.
Once cooled, melt additional chocolate chips to drizzle the top of bars with (optional). Once hardened, cut into squares.