1.  Line a 13x9-inch pan with foil, allowing foil to extend over edges of pan. Lightly coat foil with cooking spray. In a small bowl microwave half of the chocolate pieces, stirring every 30 seconds, until melted, about 1 minute. Spread evenly over the bottom of the prepared pan. Arrange split cookies, filling side down, in a single layer on top of the chocolate layer, overlapping cookies as needed to fit. Chill until chocolate is set, 30 minutes.

2. Meanwhile, in a large bowl combine chocolate-hazelnut spread, butter, and malted milk powder. Stir in marshmallow creme. Microwave 30 seconds, stirring after 15 seconds. Stir until fully combined. With lightly greased hands or a lightly greased rubber spatula, pat mixture evenly over the cookie layer in pan.

3.  In a small bowl microwave the remaining chocolate pieces, stirring every 30 seconds, until melted, about 1 minute. Immediately spread melted chocolate evenly over marshmallow layer. Chill until topping is firm, 30 minutes. Use edges of foil to lift uncut bars from pan. Transfer to a cutting board. Cut into bars.

To Store:

Layer bars between sheets of waxed paper in an airtight container; cover. Store in the refrigerator for up to 1 week or freeze for up to 1 month.