Microwave peanut butter, chocolate chips, butter and vanilla extract on high in 15-second increments, stirring in between, until just melted. Add crushed pretzels and confectioners' sugar. Using an electric mixer on medium, beat to blend. Immediately press into a foil-lined 8-inch square pan. Microwave semisweet chocolate chips at 50 percent power in 15-second increments, stirring in between, until just melted. Pour over cookie base. Decorate immediately with sprinkles and pretzels. Let stand until set, about 1 hour. Cut into 2-inch squares.
