Line 8-inch square pan with foil, and spray with cooking spray.

Place 3 cups white vanilla baking chips, 1 can (14.5 oz) sweetened condensed milk (not evaporated), and 1/2 cup peanut butter (not natural) in large microwavable bowl. Microwave uncovered on High in 1-minute increments, stirring well between each, until melted and smooth. This may take several minutes. Be careful; the bowl will get hot.

Spread immediately in pan. Let stand at least 2 hours to set before cutting, or refrigerate to speed up setting process. For 36 squares, cut into 6 rows by 6 rows. Store in airtight container, and use within 5 days