Preheat the oven to 350°F (175°C). Line a 9×9-inch baking pan with parchment paper, leaving a little overhang on the sides for easy lifting. Set aside.
To a medium microwave-safe bowl, add ½ cup of chocolate chips and the vegetable oil. Microwave in 15-second intervals, stirring between each, until the chocolate is melted and smooth. Set aside to cool slightly.
In the bowl of a stand mixer fitted with the whisk attachment, add the granulated sugar, brown sugar, eggs, vanilla, and peppermint extract. Beat on high speed for 5-6 minutes, or until the mixture is pale, thick, and has doubled in volume. Scrape down the sides of the bowl as needed.
With the mixer on low speed, slowly pour in the melted chocolate mixture. Mix until just combined.
In a small bowl, whisk together the flour, cocoa powder, and kosher salt.
Add the flour mixture to the wet ingredients and mix on low speed until just combined.
Fold in ½ cup of chocolate chips.
Pour the batter into the prepared pan, smoothing the top with a spatula. Sprinkle the remaining chocolate chips evenly over the top.
Bake for 30-35 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs but no wet batter.
Immediately after baking, sprinkle the crushed peppermint candies over the hot brownies. Cool completely in the pan on a wire rack.
Once cooled, lift the brownies from the pan using the parchment overhang. Cut into squares and serve.