• Preheat the oven to 350 degrees F. Line 2 to 3 large cookie sheets with parchment paper. Sift together the all-purpose flour, baking soda, and salt.
• Place the butter and sugar in a large bowl and beat with an electric mixer until pale and fluffy. Beat in the egg and vanilla extract followed by half of the flour mixture and then the buttermilk and food coloring. Stir in the rest of the flour mixture and mix until thoroughly incorporated.
• Pipe or spoon 28 mounds of the batter onto the prepared cookie sheets, spaced well apart to allow for spreading. Bake in the preheated oven, one sheet at a time, for 9-11 minutes until risen and just firm to the touch. Cool for 5 minutes, then using a palette knife transfer to a cooling rack and let cool completely.

For the filling:

• Place the butter and vanilla extract in a bowl and beat with an electric mixer for 2-3 minutes until pale and creamy. Beat in the cream, then gradually beat in the confectioners' sugar and continue beating for 2-3 minutes.
• To assemble, spread or pipe the buttercream on the flat side of half of the cakes. Top with the rest of the cakes.