Line a 9x13 baking dish with parchment paper. Set aside.

Beat softened butter for 1 minute until smooth. Add peanut butter and vanilla; continue mixing for 1 minute.

Lower mixer speed, add powdered sugar 1 cup at a time, mixing well after each addition. Spread mixture evenly in prepared dish.

Add chocolate chips and oil to a microwave-safe bowl. Heat for 1 minute, stir, then continue in 15-second intervals until smooth.

Spread the melted chocolate over the peanut butter layer. Chill for 15-20 minutes.

Slice into 2 ½ in x 3 in pieces. Refrigerate for an additional 1 hour 45 minutes before serving.

Remove bars from dish, re-slice if necessary, and serve immediately.