Follow the steps in order for the best result.
First, prepare the topping. In a small bowl, combine the brown sugar, cinnamon, chopped nuts, flour, and melted butter (or margarine). Mix well with a fork until crumbly. Set aside.
Grease an 8x8 inch baking pan to prevent sticking.
In a mixing bowl, cream together the butter (or margarine) and sugar until light and fluffy. Beat in the egg until well combined.
Gradually add the flour, baking powder, and salt to the creamed mixture, alternating with the milk. Mix until just combined; do not overmix.
Pour the batter into the prepared baking pan and spread evenly.
Sprinkle the prepared topping evenly over the batter.
Cover the pan tightly with plastic wrap or foil and refrigerate overnight.
The next morning, preheat your oven to 375 degrees F (190 degrees C).
Bake the coffee cake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Let the coffee cake cool slightly before cutting into squares and serving.
For an Upside-Down Coffee Cake Variation: Grease an 8x8 inch baking pan.
Add 1/4 cup of corn syrup to the spicy topping mixture and spread evenly in the bottom of the pan.
Cover with Refrigerator Coffee Cake batter.
Place in fridge overnight and bake as directed above.
Turn up-side down immediately onto a serving plate.
Enjoy your delicious coffee cake!