Heat oven to 350°F. In 1-quart heavy saucepan, heat condensed milk and peanut butter over medium-low heat 8 to 10 minutes, stirring frequently, until slightly thickened. Remove from heat; stir in vanilla until well blended. Refrigerate about 20 minutes or until thickened.
Meanwhile, in large bowl, break up cookie dough. Add peanuts and pretzels. Mix with wooden spoon, or knead with hands until well blended. Shape dough into 30 (about 1 1/4-inch) balls. Place 2 inches apart on ungreased cookie sheets. Bake 5 to 10 minutes or until edges are light golden brown. Remove from oven; immediately press back of teaspoon into center of each cookie to make indentation. Cool 2 minutes; remove from cookie sheets to cooling racks. Cool completely, about 20 minutes.
Place peanut butter mixture in large resealable food-storage plastic bag. Cut off small corner of bag. Squeeze bag to pipe about 1 tablespoon mixture in center of each cookie to fill indentation.
In small microwavable bowl, microwave chocolate chips uncovered on High 40 to 60 seconds, stirring once, until chips can be stirred smooth. Place melted chips in small resealable food-storage plastic bag. Cut off tiny corner of bag. Squeeze bag to drizzle melted chips over cookies. Let stand 10 minutes. Store covered.