Preheat the oven to 350 degrees F (175 degrees C). Grease and flour two 9-inch round cake pans.
Combine brown sugar, flour, and cinnamon in a bowl; mix with an electric mixer until sugar clumps are broken up. Add melted butter; mix until thoroughly blended. Stir in pecans by hand. Set filling aside.
Blend sifted flour, baking powder, and salt together in a large bowl. Combine sugar, shortening, and egg in a second large bowl; mix with an electric mixer until thoroughly combined. Add milk and mix on low speed. Stir in dry ingredients.
Spread 1/4 of batter into each of the prepared cakes pan and spread 1/4 of streusel filling over each. Repeat once more, spreading layers evenly.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 25 to 30 minutes.
