Combine brown sugar and 1 tablespoon flour in a bowl, mix and set aside. Combine 1 1/4 cups flour with the granulated sugar, pecans, baking powder and salt in a bowl, make well in the center.
Combine milk, margarine, and vanilla and add to flour mixture, stir until moist. Spread batter into an 8 inch square baking pan, sprinkle top with brown sugar mixture. Pour boiling water over batter, do not stir.
Bake at 350 for 35 minutes or until pudding is bubbly and cake springs back when lightly touched in center.
Serve warm with whipped cream topping.
Garnish with pecans if desired.
I made this cake this past weekend, it is not too heavy as I got it from Cooking Light Magazine.