Pumpkin Spice Peanut Butter Cookies

1. In a medium bowl, whisk together the flour, baking powder, and salt.
2. In the bowl of a stand mixer fitted with the paddle attachment (or using a bowl and handheld electric beater), cream together the butter and brown sugar. Add the egg and egg yolk one at a time, beating each in until well-incorporated. Beat in the peanut butter and vanilla extract until smoothly combined, wiping down the bowl and beater as needed.
3. Add the dry ingredients to the wet and fold in just until evenly incorporated. Transfer cookie dough to an airtight container and chill in refrigerator for at least a few hours, or overnight.
4. To shape cookies, scoop dough by 3/4 ounce portions and roll each portion into a ball. Place on a parchment lined baking sheet and flatten with palm of hand to form a round just over 2 1/4" wide. Use a 2 1/4" cookie cutter to trim off uneven edges. Repeat with remaining dough. Chill cookies on prepared baking sheets for another 15 minutes prior to baking. Meanwhile, preheat oven to 350ºF.
5. Just before baking, use a fork to press a criss-cross pattern into the center of each cookie. Bake cookies for 6-7 minutes, until tops have puffed slightly and no longer look glossy/wet. Allow cookies to cool completely before dipping in chocolate.
6. Place chocolate in a liquid measuring cup or other similarly shaped microwave-safe container and microwave for 1 minute. Stir and continute to melt for 30-second increments, stirring in between, until chocolate is smoothly melted. Dip each cookie halfway in chocolate and return to parchment-lined baking sheet. Refrigerate cookies until chocolate has set.*

Marshmallow Filling

1. In the bowl of a stand mixer fitted with the wire whip attachment, combine the egg whites, cream of tartar, and salt and beat until soft peaks form.
2. Meanwhile, combine the sugar and water in a small saucepan and heat over moderately high heat, stirring constantly, until sugar has dissolved.
3. With mixer at medium speed, slowly pour the sugar syrup into the egg whites from the side of the bowl. Continue beating until filling is fluffy and has cooled to room temperature.
4. Spoon filling onto half of cookies or use a piping bag fitted with a large round tip (I used Ateco #808) to pipe onto half of cookies. Sandwich with remaining cookies and refrigerate until filling has set. Store in an airtight container in the refrigerator until ready to serve.