Preheat the oven to 350° F and spray an 8 or 9-inch baking pan with cooking spray. Set aside.

In a large mixing bowl, cream the butter and sugar by hand or with a hand mixer until light and fluffy. Add the eggs one at a time and beat to combine. Add the dry ingredients alternately with the milk, starting with the flour, then baking powder, cinnamon and salt, then oatmeal. 

Scrape and pour the batter into the prepared pan and bake for 35 to 40 minutes. Remove from the oven and set aside to cool slightly. Carefully move an oven rack to about 5 inches below the broiler element. Preheat the broiler.

Topping and Glaze

While the cake is baking, cream 1/4 cup butter and brown sugar. If using frozen orange juice concentrate, add it at this point. If using orange juice, in a small saucepan simmer over medium heat for about 15 minutes, stirring occasionally, until reduced by half before adding it to the butter/brown sugar mixture. Add the chopped nuts.

Spread the topping over the warm cake and place it under the broiler for about 2 minutes, or until the topping is bubbly. Cool slightly before serving.

Best served warmed, or heated slightly in the microwave. Refrigerate any leftovers.