- For the brownies, preheat the oven to 350°F. Grease and line a 9 x 13-inch pan with parchment paper, so that the paper comes up the sides.
- Melt the butter and chocolate in a sauce pot over low heat, stirring constantly until smooth. Scrape it into a large mixing bowl and, while still warm, whisk in the vegetable oil, granulated and brown sugars, and then whisk in the eggs and vanilla. Sift the flour, cocoa powder and salt in a separate bowl, then whisk into the brownie mixture. Stir in the crushed pretzels and chocolate chips, then scrape the batter into the prepared pan and spread evenly. Bake the brownies for about 30 minutes, until the surface of the brownies takes on a matte appearance. Allow the brownies to cool in the pan before frosting.
- For the frosting, beat the butter and peanut butter together until light and fluffy. Add the icing sugar and vanilla and beat well until smooth. Spread this evenly over the brownies. The brownies are best served at room temperature, but are more easily sliced after being refrigerated for an hour. Once sliced, place a pretzel twist on each brownie for decor.
The brownies will keep in an airtight container for up to four days.