Preheat the oven to 350°F. Line a baking sheet with parchment paper. Set aside.

In a stand mixer fitted with the paddle attachment, beat together the peanut butter, butter and brown sugar on low speed until combined. Gradually increase to medium-high and beat until light and fluffy, about 1 minute.

Use a silicone spatula to scrape down the bowl, then add in the egg and vanilla. Beat to combine.

Add the flour, cornstarch, baking soda, and salt and beat on low speed until just combined.

Use a 1 ounce cookie scoop to portion out equal amounts of dough. Shape the dough balls into flat oval discs and place on the baking sheets, spacing 2 inches apart.

Use a fork to make crosshatches on each circular end of the dough.

Bake for 9 to 10 minutes or until puffed up and set around the edges but still soft in the middle.

Remove from the oven and allow the cookies to cool completely.

In a stand mixer fitted with the paddle attachment, combine the peanut butter, powdered sugar, 3 tablespoons of heavy cream, and vanilla extract. Beat on low speed until smooth.

If filling is too thick, add the last tablespoon of cream. Transfer to a piping bag.

Match up cooled cookies into pairs. Pipe filling onto the bottom of one half and sandwich together with the other half.