Step 1: Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone baking mats.
Step 2: In a medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, ground ginger, ground nutmeg, and salt. Set aside.
Step 3: In a large bowl, using an electric mixer, cream together the softened unsalted butter, granulated sugar, and packed light brown sugar until light and fluffy, about 2-3 minutes.
Step 4: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 5: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined. Be careful not to overmix.
Step 6: Gently fold in the grated carrots by hand, ensuring they are evenly distributed throughout the batter.
Step 7: Drop rounded tablespoons of batter onto the prepared baking sheets, leaving about 2 inches between each. A cookie scoop is recommended for uniform size.
Step 8: Bake for 10-12 minutes, or until the edges are lightly golden and the centers spring back when gently touched. Transfer the cookies to a wire rack to cool completely.
Step 9: While cookies cool, prepare the frosting. In a large bowl, beat the softened cream cheese and softened unsalted butter together with an electric mixer until smooth and creamy, about 2-3 minutes.
Step 10: Gradually add the sifted powdered sugar, one cup at a time, mixing on low speed until combined, then increase speed to medium-high and beat until light and fluffy. Add the vanilla extract and a pinch of salt, beating for another minute.
Step 11: Once the cookies are completely cool, spread a generous amount of cream cheese frosting onto the flat side of half of the cookies. Top with the remaining cookies, flat side down, to create a sandwich.
Step 12: For optimal flavor and texture, refrigerate the assembled whoopie pies for at least 30 minutes before serving. Store any leftovers in an airtight container in the refrigerator.