Preheat the oven to 350 F and line two baking sheets with parchment paper.

Whisk the flour, baking soda and salt together in a medium bowl and set aside.

Beat the butter and sugar together until pale and fluffy, about 2 minutes, then beat in the egg.

Add the flour mixture and buttermilk alternately, mixing just until combined, then stir in green food coloring until bright.

Drop the batter by 2 tablespoon mounds onto the sheets, spacing them 2 inches apart.

Bake for 10 to 12 minutes, until the tops spring back when touched lightly, then cool completely on the sheet.

Beat the cream cheese, butter and powdered sugar together for the filling until smooth and spreadable.

Spread or pipe filling onto the flat side of half the cakes, press a red heart sprinkle into the exposed edge, and top with a second cake.