Add 2-3 tablespoons of cold brew concentrate and the dulce de leche to a small bowl or Mason jar. Mix vigorously until the dulce de leche is completely combined.
Divide the dulce de leche mixture between two 12 ounce mason jars. Add ice. Add the cold brew concentrate to the mason jars and top with milk.
Mix to combine and drink immediately.
Cold brew coffee concentrate – About 1/2 cup, divided
Dulce de leche – 4-5 tablespoons