Preheat your oven to 350ºF
Line an 8-inch square baking pan with parchment paper, allowing it to hang over two sides. Coat the paper with cooking spray
In a stand mixer fitted with the whisk attachment, whisk together the melted butter with the sugar and light brown sugar until smooth, about 2 minutes
Add the eggs and vanilla and whisk until combined
Remove the bowl from the stand mixer and stir in the flour and salt just until incorporated.
Stir in 1 cup of the chocolate chips and 1/2 a cup of the crushed pretzels
Pour the batter into the prepared pan, smoothing the top
Sprinkle the remaining 1/2 cup of crushed pretzels on top, pressing them lightly into the batter
Bake for 35 - 40 minutes until a toothpick inserted comes out clean
While the cookie bars are baking, melt the remaining 1/2 cup chocolate chips with the vegetable oil in a double boiler or in the microwave
Remove the cookie bars from the oven and allow them to cool completely in the pan then remove the cookies using the parchment paper overhang
Drizzle the cookie bars with the melted chocolate and allow them to cool until the chocolate hardens
Cut the cookie bars into 16 squares and serve
