Place the 10-ounce bag of snack-sized Reese's Peanut Butter Cups in the freezer for about 30 minutes.

Line a 9 x 9-inch pan with non-stick foil, or line with foil and spray the foil with non-stick cooking spray; set the pan aside.

Put 6 cups Rice Krispies cereal into a large bowl and set aside.

In a medium saucepan, combine 1 cup sugar and 1 cup light corn syrup. Heat over medium, stirring, until the sugar dissolves. Do not allow the mixture to boil. Remove the pan from the heat as soon as the sugar is dissolved.

Stir 1 cup creamy peanut butter and 1 teaspoon vanilla into the hot syrup mixture until smooth and fully combined.

Pour the peanut butter mixture over the cereal. Stir gently but thoroughly until the cereal is evenly coated.

Transfer about half of the coated cereal mixture into the prepared pan. Use a spatula or the back of a spoon to gently press it into an even layer.

Arrange the frozen Reese's Peanut Butter Cups in a single layer on top of the pressed cereal base, spacing them evenly.

Press small amounts of the remaining cereal mixture into the spaces between the peanut butter cups. Spread the rest of the cereal mixture over the cups and press gently until the top is even and the cups are mostly covered.

Allow the bars to cool and set at room temperature until firm (about 30 minutes), or refrigerate for 10–15 minutes to speed setting.

Lift the bars from the pan using the foil, place on a cutting board, and cut into squares or bars to serve.