Preparation Steps

• Line two baking sheets with parchment. Set oven to 340°F (170°C). Pop the marshmallows into the freezer to firm up while you make the dough; this slows their melting.
• In a medium bowl, whisk together the flour, baking soda, baking powder, and fine sea salt until evenly combined.
• In a large bowl with a hand mixer (or stand mixer), beat the softened butter, creamy peanut butter, and honey on medium-high until fluffy, about 2 minutes.
• Add the brown sugar and granulated sugar and beat 1 minute more. Mix in the egg and egg yolk just until smooth, then blend in the milk and vanilla on low speed.
• Add the dry ingredients to the bowl and mix on low until the flour is just incorporated. Cover and let the dough rest for 15 minutes to hydrate; it will thicken slightly and scoop more cleanly.
• Scoop heaping tablespoonfuls (about 1 1/2 tablespoons each) onto the prepared sheets, spacing 2 inches apart. Gently press each mound to about 3/4-inch thick. Par-bake for 6 minutes to set the edges.
• Remove the pans from the oven. Working quickly, press one cold marshmallow into the center of each cookie. Return to the oven and bake 6 to 7 minutes more, until the edges are set and the marshmallows show light golden spots.
• Cool on the baking sheet for 8 to 10 minutes to firm up, then transfer to a rack. While still warm, finish with a tiny pinch of flaky sea salt on each cookie.