Preheat the oven to 350F.
Sift the flour and set it aside.
Chop black walnuts if necessary.
Place butter in a large mixing bowl.
Add lard or shortening.
Use a mixer to blend butter and shortening for 3 minutes.
Gradually mix in light brown sugar until smooth.
Add granulated sugar gradually, mixing until light and fluffy.
Add eggs one at a time, mixing until combined; scrape the bowl as needed.
Alternate adding flour and milk, starting and ending with flour.
Incorporate butter nut flavoring, mixing until combined.
Add the walnut pieces.
Gently fold the nuts into the mixture by hand until combined.
Grease and flour three 8-inch cake pans.
Divide the batter among the three pans.
Bake at 350F for 20-30 minutes or until a wooden toothpick comes out clean.
Remove from the oven and place the pans on a wire rack to cool for 10 minutes.
Remove the layers from the pans and transfer them to a wire rack to cool completely.