Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a medium bowl, combine the melted butter, flour, and granulated sugar for the crust. Mix until well combined and it forms a crumbly dough. Press evenly into the bottom of the prepared baking pan.
Bake the crust for 10-12 minutes, or until lightly golden brown.
While the crust is baking, prepare the caramel pecan topping. In a saucepan over medium heat, combine brown sugar, butter, and corn syrup. Stir constantly until the butter is melted and the mixture is smooth. Bring to a boil, then reduce heat and simmer for 2-3 minutes, stirring occasionally.
Remove from heat and stir in the vanilla extract and chopped pecans. Pour the caramel pecan mixture evenly over the hot baked crust.
Return the pan to the oven and bake for another 15-18 minutes, or until the caramel is bubbly and golden brown.
Let the bars cool completely in the pan on a wire rack.
Once cooled, prepare the chocolate drizzle. In a microwave-safe bowl, combine chocolate chips and vegetable oil. Microwave in 30-second intervals, stirring between each, until melted and smooth.
Drizzle the melted chocolate over the cooled bars in a decorative pattern.
Allow the chocolate to set completely before cutting into bars.
Notes
For best results, ensure the bars are completely cooled before cutting to prevent the caramel from oozing out.