Preheat the oven: Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats.

1. Mix the wet ingredients: In a large bowl, beat together the softened butter, peanut butter, and granulated sugar until light and fluffy (about 2-3 minutes).
2. Add the egg and vanilla: Beat in the egg and vanilla extract until fully incorporated.
3. Combine dry ingredients: In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing just until combined.
4. Shape the cookies: Scoop out dough and roll it into balls. Place on the baking sheets, spacing them about 2 inches apart. Flatten the dough with a fork, creating a criss-cross pattern.
5. Bake the cookies: Bake for 8-10 minutes, or until lightly golden around the edges. Remove from the oven and let cool for a minute.
6. Add the jelly topping: Using the back of a spoon, make a small indent in the center of each cookie. Spoon about 1 teaspoon of jelly into the center of each cookie.
7. Cool and serve: Let the cookies cool completely on the baking sheet before serving.