Beat the peanut butter and butter with an electric mixer in a large bowl until smooth. Beat in the sugar and vanilla. Cover and refrigerate for 30 minutes. Roll chilled mixture into small, eyeball-sized balls and place on 2 baking trays lined with greaseproof paper. Refrigerate for another 30 minutes.
Melt the white chocolate and butter in a microwave-safe glass or ceramic bowl in 30-second intervals, stirring after each melting, for 1 to 3 minutes (depending on your microwave). Do not overheat or chocolate will scorch. Dip each eyeball into the white chocolate and transfer to the greaseproof paper until the chocolate has set. You can chill them in the refrigerator.
Stir a few drops of blue food colouring into the remaining melted white chocolate. Make a round "iris" on the top of the cooled eyeball and press a mini chocolate chip in the centre for a "pupil". For extra spooky bloodshot eyeballs, take a skewer dipped in red food colouring and make squiggly lines on the eye.