Whisk together sweetened condensed milk and mint extract in a large bowl.
Whip heavy cream on medium-high speed with an electric mixer until stiff peaks form. Fold whipped cream into sweetened condensed milk mixture.
Spread a layer of ice cream into the bottom of a 9x5 loaf pan. Top with 1/3 of chopped Thin Mints. Drizzle with ganache. Repeat layers two more times, ending with cookies and ganache on top.
Freeze for about 6 hours, or overnight.