Preheat the oven to 325 degrees F. Spray two 9 X 5 loaf pans with nonstick cooking spray.
Place 3 sticks butter and 2 1/2 cups brown sugar in the bowl of an electric mixer. Beat on high to cream the butter and sugar together until light and fluffy, about 3-5 minutes. Scrape the bowl, then mix in the eggs, 1 cup milk, 2 teaspoons vanilla extract, salt and baking powder. Slowly add in the flour. Scrape the bowl, then beat until smooth.
Divide the batter into the two loaf pans. Bake for 65-80 minutes, until a wooden skewer inserted into the center comes on clean. Cool in pans for 10 minutes. Then flip out onto a cooling rack.
Once the cakes are out of the oven, place the remaining 1 stick of butter, 1/2 cup of brown sugar, and 1/4 cup milk in a small sauce pot. Heat over medium heat until the mixture comes to a low boil. Boil for 4-5 minutes, then remove from heat and whisk in 1 teaspoon vanilla and 2 cups powdered sugar. Whisk until smooth, then stir in the pecan pieces.
While the praline mixture is still warm, pour it over the top of both pound cakes. Allow them to cool to room temperature before cutting or wrapping.