Preheat oven to 350 degrees. Lightly grease an 8x8-inch square pan. Line the pan with parchment paper leaving the extra hanging over the sides.

In a food processor combine the pretzels and graham crackers. Pulse until crushed. You should have about 1 1/4 cups of crushed pretzels and crackers. In a medium mixing bowl, combine the melted butter and the granulated sugar. Add the crushed pretzel mixture and stir until combined. Gently press the crust mixture into the bottom of the prepared pan. Don't press too hard! Bake at 350 degrees for 10 minutes. Cool completely before filling.

For the filling beat the cold whipping cream in a medium bowl until stiff peaks form. Set aside.

In another medium mixing bowl combine the sweetened condensed milk, lime juice, tequila and Cointreau. Gently fold in the whipped cream, just until blended.

Pour the filling into the prepare crust and freeze for about 4 hours or overnight. Garnish with a mixture of lime zest and sugar if desired. Cut into 9 to 12 servings.