Heat the oven to 350°F. Line two large baking sheets with parchment paper.

Whisk the flour, baking soda, baking powder, kosher salt, cinnamon, nutmeg, and ginger in a medium bowl.

In a large bowl, whisk the melted butter, brown sugar, and granulated sugar until smooth. Whisk in the egg and vanilla.

Stir in the grated carrots.

Add the dry mixture and stir just until no dry flour remains.

Scoop 2-tablespoon portions onto the prepared sheets, spacing them about 2 inches apart.

Bake 10 to 12 minutes, until the edges look set and the centers still look slightly soft.

Cool on the sheets for 5 minutes, then move to a wire rack and cool completely.

Beat the cream cheese and butter until smooth, scraping the bowl as needed.

Mix in the marshmallow fluff, vanilla, and salt until combined.

Add the confectioners’ sugar 1 cup at a time on low speed. Once it is incorporated, beat on medium speed for about 1 minute, until light.

Chill the filling for 20 to 30 minutes if you want a firmer, pipeable texture.

Spread or pipe filling on the flat side of half the cookies. Top with the remaining cookies and press gently.