Preheat the oven to 375 degrees F.
In a large bowl beat the carrot cake mix, butter, and eggs until incorporated. Stir in the grated carrot, and raisins. Refrigerate for at least 30 minutes or up to 2 hours. Using a small ice-cream scoop drop the batter by 2 tablespoon mounds onto parchment lined cookie sheets. Bake until golden brown, about 10 to 12 minutes, rotating the pans halfway through. Remove and cool 5 minutes on the pan before moving to a wire rack and cooling completely.
In a mixing bowl beat together the cream cheese, butter, confectioners' sugar, and vanilla with a hand mixer until well combined and light and fluffy.
To assemble the whoopie pies, put the filling into a resealable bag and snip the corner to make a 1/2-inch opening. Put the chopped walnuts into a shallow dish or pie plate. Flip over 1 carrot cake cookie and pipe a dollop of frosting into the center. Top with another cookie and press gently to spread the frosting to the edges. Roll the edges of the whoopie pie into the chopped walnuts and set aside. Repeat with the remaining cookies and frosting. Arrange the pies on a serving platter and serve.