Beat the butter, granulated sugar, and brown sugar together for a full 2–3 minutes until light and fluffy. This is where the structure starts.
Mix in the egg, vanilla, and cornstarch until fully combined. The cornstarch keeps these easy peanut butter cookies with jelly soft without turning them fragile. Add in the peanut butter and mix until smooth.
In another bowl, whisk flour, baking soda, baking powder, and salt.
Gradually add dry ingredients to wet mixture. Mix just until combined. Do not overwork the dough.
Scoop about 1 ½ Tablespoons of dough and roll into smooth balls. Place 2 inches apart.
Flatten each ball gently using a fork in a criss-cross pattern. This is what gives authentic PB&J cookies their traditional look.
Using your thumb or a ¼ Teaspoon, create a small centered well in each cookie.
Spoon 1 teaspoon of seedless jam into each indent. Don’t overfill - jam expands and will sink into the cookie.
Bake at 350 degrees Fahrenheit for 13–15 minutes.
Edges should be golden. Centers should be set. Do not underbake.
Allow cookies to sit on the baking sheet 5–10 minutes before transferring to a cooling rack. Re-indent right after baking if the center puffs up - gently press again while warm.
Finish like a boss (garnish): Once cookies are completely cool, add a small spoonful of extra jam to the center, drizzle 2–3 Tbsp warmed peanut butter over the top, and sprinkle chopped dry roasted peanuts if desired .. turning them into bakery-worthy easy peanut butter cookies with jelly.