In a medium saucepan, combine the butter, sweetened condensed milk, and white chocolate chips. Cook over medium-low heat, stirring constantly, until smooth and fully melted. Remove from the heat.
Stir in the vanilla, ½ cup of the crushed cookies, and ½ cup of the mini chocolate chips. Mix just enough to combine, leaving streaks of chocolate for a marbled look.
Pour the mixture into a parchment-lined 8×8-inch baking dish. Sprinkle the remaining crushed cookies and mini chocolate chips over the top.
Refrigerate for at least 2 hours, or until firm. Slice into squares and serve.
Notes
Stir just enough to create chocolate swirls instead of fully mixing them in.
Any chocolate chip cookies work well for this recipe.
Store in an airtight container for 3–4 days at room temperature or up to 2 weeks in the refrigerator.
Try different cookies and toppings, like peanut butter cookies or shortbread with a raspberry drizzle, to create your own variation.