In a medium bowl, beat together the egg, maple syrup, heavy cream, and vanilla. Add the wet ingredients to the baking mix and beat until well incorporated but not over mixed, about 1 minute. Gently stir in the chopped walnuts. Using an ice cream scoop, fill the muffin tins about 2/3 full. Bake until golden brown and a toothpick inserted into the center comes out clean, about 10 to 12 minutes. Cool for 1 minute before removing the cakes from the pan and cooling completely on a wire rack.