Line a baking sheet with parchment paper and evenly distribute the Ritz crackers in a single layer across its surface.

Place the sweetened condensed milk, brown sugar, and butter into a small saucepan set over medium heat. Stir the mixture regularly as it cooks for 7 to 8 minutes, ensuring it does not burn.

Once the mixture begins to thicken, reduce the heat to low and incorporate the milk, vanilla extract, and chopped peanuts, whisking until the mixture is smooth. Continue to cook for an additional 2 minutes or until the consistency becomes rich and thick.

Remove the pan from heat and, using a cookie scoop or spoon, drop portions of the caramel-peanut mixture onto each cracker.

Let the cookies cool completely on the baking sheet. Once cooled, transfer them to an airtight container for storage.