Preheat the oven to 350 degrees F. Line a 12 cup muffin tin with paper liners.
In a large bowl, measure out 2 cups of baking mix, and set aside.
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.
Glaze: Stir together the confectioners' sugar, pumpkin pie spice, maple syrup, and heavy cream in a medium bowl. Whisk the mixture slowly until it becomes a thick but pourable mixture, adding more heavy cream as needed. Dip the cakes into the icing bowl to coat the top, and garnish each with a walnut half. Arrange them on a serving platter and serve.