Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, cream butter and sugar until light and fluffy.
Mix in egg yolk, vanilla extract, peppermint extract, and food coloring if using.
Add flour and salt and mix just until a soft dough forms.
Roll dough into 1-tablespoon balls and place 2 inches apart on baking sheets.
Use your thumb or the back of a teaspoon to gently press an indentation into each cookie.
Bake for 11–13 minutes, until edges are set but centers remain pale.
Cool cookies on the baking sheet for 5 minutes, then transfer to a wire rack.
Heat heavy cream until just steaming, then pour over chocolate chips. Let sit 1 minute, then stir until smooth.
Spoon ganache into each cookie center and immediately sprinkle with crushed Oreos.
Let ganache set before serving.