Preheat the oven to 350℉. Line two baking sheets with parchment paper or a silicone baking mat.
In a large bowl or stand mixer, beat 1/2 cup butter until it is smooth and creamy, scraping the sides of the bowl.
Add ¾ cup sugar and ¼ cup packed brown sugar. Beat well until fluffy, scraping the sides. There should be no chunks of butter.
Add 1 cup peanut butter and beat well until combined. Then add 1 egg and 1 teaspoon vanilla. Mix until well combined.
Add 1½ cups all-purpose flour, but don't stir it in yet. Add 1 teaspoon baking soda and ¼ teaspoon kosher salt on top of the flour. Stir it in with your teaspoon to combine the dry ingredients together a bit.
Turn the mixer on to combine the dry ingredients into the dough. Don't overdo it! Once the dough barely starts to come together (with some flour still visible), stop and scrape the sides and bottom of the bowl. Continue mixing until you no longer see flour streaks, then turn off the mixer. Over mixing cookie dough results in tough cookies.
Shape the dough into 1½ inch balls and place each cookie on a baking sheet with about a couple inches of space in between.
Dip a fork into a bit of sugar or flour (to make sure it doesn't stick too much to the dough) and press into the top of a cookie. Turn the fork perpendicular and press one more time. Smash them to about ½ inch thickness. Dip in sugar whenever the fork starts to stick to the dough.
Add ½ cup seedless jam to a bowl and stir well to get out most of the lumps. Use a teaspoon to carefully add 1 teaspoon (or less) of jam to the top of each cookie. Do not let the jam slide off the edge, you want it right in the center. If it touches the pan it will spread and get gummy. It's not the end of the world, but try your best to keep it on top.
Bake the cookies for about 13-15 minutes. The cookies are done baking when the edges are set.
Let the cookies set on the pan for at least 5-10 minutes before transferring to a wire rack to cool completely.
Enjoy!
