In a bowl, whisk together the melted butter, peanut butter, brown sugar and granulated sugar, until smooth.
Add the egg, egg yolk and vanilla, and whisk again until smooth.
In a separate bowl, sift together the flour, corn starch, baking soda, salt and cinnamon. Add the dry ingredients to the wet, and use a spatula to stir the dough together until combined.
Dollop the jam over the cookie dough, and cut the spatula through the dough a few times, to swirl the dough throughout. You don't want to mix the jam in too much, so leave lots of visible swirls of jam.
Cover the bowl and chill the dough for 1 hour.
Preheat the oven to 375 F, and position a rack in the center of the oven. Line a baking sheet with parchment paper.
Use a medium cookie scoop (for small cookies) or large cookie scoop (for medium cookies) to scoop the dough into evenly sized portions. Slightly flatten the balls of dough with your palm.
Space the dough balls 2-3 inches apart on the baking sheet. Bake the cookies for about 9-10 minutes (for small cookies) or 12-13 minutes (for medium cookies), until the cookies have spread and the centers are mostly set. Cool the cookies on the baking sheet for 5 minutes, then transfer to a cooling rack to cool completely.
Store cooled cookies in an airtight container at room temperature for up to 5 days.