Instructions

• Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper and set aside.
• In a medium bowl, whisk together 2 ½ cups all-purpose flour, 1 ½ teaspoons salt, 1 ¼ teaspoons baking soda, and ½ teaspoon baking powder. Set the dry mixture aside.
• In the bowl of a stand mixer fitted with the paddle attachment (or in a large bowl using a handheld mixer), beat 1 ½ cups granulated sugar, 1 cup unsalted butter (room temperature), and ¼ cup shortening (if using; or substitute with the extra ¼ cup butter) on high speed for about 1 minute, until smooth and fluffy.
• Add 2 large eggs + 1 yolk, ⅓ cup Marshmallow Fluff (optional), and 1 teaspoon vanilla extract to the creamed mixture. Beat until incorporated and smooth.
• Add the reserved dry mixture and ⅔ cup crushed Lucky Charms cereal (cereal pieces only) to the mixer. Mix on low speed just until combined; do not overmix.
• Decide whether to make plain cookies or green marbled cookies: - For plain cookies: fold 1 ½ cups marshmallow pieces (from Lucky Charms cereal) into the entire dough until evenly distributed, then continue to step 8. - For green marbled cookies: transfer about 1/3 of the dough into a separate small bowl. Add a small amount of green food coloring to that portion and mix until evenly colored. Fold 1 ½ cups marshmallow pieces into the remaining (larger) uncolored dough only. Then continue to step 7.
• (Green marbled assembly) For each cookie, scoop 1 tablespoon of green dough and 2 tablespoons of the plain dough. Gently roll the two pieces side-by-side until they adhere but are not fully mixed; form into balls and slightly flatten to about 2-inch discs. Place discs on the prepared baking sheet about 3 inches apart. Press several marshmallows into the top of each disc.
• (Plain cookie assembly) Using a large 3-tablespoon cookie scoop, portion 3-tablespoon balls from the plain dough. Lightly flatten each ball into a 2-inch disc. Place discs on the prepared baking sheet about 3 inches apart. Press several marshmallows into the top of each disc.
• Bake the cookies one sheet at a time on the center oven rack for 18–20 minutes, rotating the baking sheet halfway through baking for even browning. For a flatter, chewier cookie, you may (optionally) give the baking sheet a firm slap onto the oven rack every few minutes after the cookies have baked for about 10 minutes. Remove the cookies when the tops look slightly glossy and are just set (they will firm as they cool). Do not overbake.
• Allow the baked cookies to cool on the baking sheet for about 10 minutes, then transfer them to a wire rack to cool completely.
• Store cooled cookies in an airtight container at room temperature for up to 5 days, or freeze for up to 4 months. Unbaked cookie dough balls can also be frozen in an airtight container or zip-top bag for up to 4 months; when baking from frozen, add 1–2 minutes to the baking time.