In a large microwave-safe bowl, combine semi-sweet chocolate chips, creamy peanut butter, butter, and vanilla extract. Heat this mixture in the microwave for 60-90 seconds on high, watching closely until the chocolate is melted. Stir gently until smooth and glossy.

Pour in the Chex cereal and carefully fold it into the chocolate-peanut butter mixture until evenly coated.

Line a 9x13 inch baking dish with parchment paper. Spread the coated cereal mixture evenly into the dish and press down firmly.

Refrigerate for 60-90 minutes to allow the bars to firm up.

Remove the bars using the parchment overhang and cut into squares. Toss each bar in powdered sugar until fully coated.

Store in an airtight container in the refrigerator for up to one week.