Line a baking sheet with parchment and lay out Ritz crackers in a single layer.

Combine condensed milk, butter, and brown sugar in a saucepan. Cook over medium heat for 7–8 minutes, stirring often.

Reduce heat to low and whisk in milk, vanilla extract, and peanuts. Cook 2 more minutes until thick and gooey.

Spoon the warm caramel-peanut mixture over each cracker.

Let cool completely before storing in an airtight container.