Preheat the oven to 350F and line a baking sheet with parchment paper. Set aside.
In a large bowl, beat the butter, peanut butter, and both sugars together until light and fluffy.
Scrape down the bowl and add the egg, egg yolk and vanilla. Mix well.
In a separate bowl, sift together the flour, baking soda, baking powder, and salt. Add the dry ingredients to the wet ingredients and mix until just combined.
Scoop dough into ~2 inch balls (60g). Roll dough balls in granulated sugar and place on the prepared baking sheet ~2 inches apart.
Bake at 350°F for 12–14 minutes or until the cookies have puffed up and are set on the edges, but still gooey in the middle.
Allow to cool for 5 minutes on the baking sheet, then transfer to a cooling rack and sprinkle with flaky sea salt.
While the cookies fully cool, melt your chocolate wafers in the microwave or over a double boiler. Once the chocolate is melted, spoon about ½ Tbsp onto parchment paper and immediately place a cooled cookie on top, pressing down lightly until the chocolate reaches the cookie’s edge.
Allow the cookies to rest for 3–5 minutes until the chocolate has set. If desired, drizzle additional melted chocolate on top of each cookie. Enjoy!
