Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, combine butter and sugar until smooth.
Add in the egg and peppermint extract, and mix until smooth. Add in the flour mixture, and mix until it is all combined. Fold in crushed candy canes and crushed Oreo cookies.
Press the cookie dough into a greased 8-inch square baking dish. Bake for 15-20 minutes.