Preheat oven to 350 degrees. Lightly grease an 9 by 12 baking pan. Set aside.
Sift together 1 ½ cups all-purpose flour, 1 cup unsweetened cocoa powder and ½ teaspoon kosher salt. Set aside.
In a large mixing bowl with the paddle attachment (a handheld mixer works fine) mix together 1 ½ cup packed light brown sugar, 1 ½ cups granulated sugar, 1 cup melted unsalted butter (that's been cooled) and 1 ½ Tablespoons of vanilla extract. Mix until completely combined.
Add in 4 large eggs, one at a time. Let each one incorporate before adding the next one.
Slowly add in the dry ingredients. Mix until almost combined.
Take a spatula/mixing spoon and fold the ingredients together. Set aside.
Chop 1 ½ large Ghirardelli Dark Chocolate Peppermint Bark bars into pieces. Don't chop the chocolate into too small of pieces. Throw the chocolate pieces into the brownie batter.
Using a spatula/mixing spoon, fold the chocolate pieces into the brownie batter.
Spread evenly into the baking pan. Bake at 350 degrees for 30 minutes.
Once the brownies are done, cool them on a cooling rack until almost completely cool.
While the brownies are cooling, unwrap 12 individual Ghirardelli dark chocolate peppermint bark squares.
Then lightly press the individual square into the brownies when the brownies are almost cool. If you press them in while they're still really warm, the chocolate will melt too much.
Cut into squares and enjoy!