Preheat oven to 350F. Line two baking sheets with parchment paper and set aside.
Place butter and sugars in the bowl of a large stand mixer, fitted with a paddle attachment OR in a large mixing bowl with a wooden spoon. Mix on medium speed or by hand until creamy, about 2 minutes. Add peanut butter, egg, and vanilla and mix until smooth.
In a small bowl, combine flour, baking soda, and salt. Mix flour mixture into peanut butter mixture until dough is just combined.
Wrap dough in plastic wrap and chill in refrigerator 2 hours or up to 6 days.
Remove dough from refrigerator and preheat oven to 350F. Scoop dough into 1 inch balls and space 2 inches apart on prepared baking sheets. Optionally, roll dough balls in sugar. Use a fork to make a criss-cross indention in each ball, flattening them slightly.
Bake cookies at 350F 10-12 minutes until edges of cookies are golden brown. Cool cookies on baking sheet 10 minutes before transferring to a wire cooling rack to cool completely.
Whipped Chocolate Ganache
Place chocolate in the bowl of a stand mixer. Heat heavy cream over medium heat until steaming (do not boil). Pour heavy cream over chocolate and whisk until chocolate is melted. Whisk in vanilla and salt.
Allow chocolate mixture to sit at room temperature 1 hour until slightly set and the consistency of melted peanut butter.
Attach a whip attachment to bowl and whip chocolate mixture on high until it reaches stiff peaks.
Spread chocolate filling on the bottom of half of the cooled peanut butter cookies. Take remaining peanut butter cookies and place on top to form a sandwich. Enjoy!
Notes
Storing InstructionsStore cookie sandwiches in an airtight container at room temperature to 2 days.