Heat the oven to 350°F and line a baking sheet with parchment paper.
In a mixing bowl, beat the peanut butter, butter, granulated sugar, and brown sugar until smooth and creamy.
Add the egg and vanilla extract, then mix until fully combined.
Stir in the flour, baking soda, and salt until a soft dough forms.
Scoop the dough into 12 equal portions and roll each into a ball. Place the balls on the prepared baking sheet and flatten slightly with your palm.
Bake for 9 to 11 minutes until the edges look set. Remove from the oven and let the cookies cool on the sheet for 5 minutes.
While the cookies are still warm, gently press one candy eyeball into the center of each cookie.
Once the cookies have cooled completely, use the red decorating gel to draw short lines around each eyeball to create veins.