Preheat oven to 350 degrees.
In a microwaveable bowl, combine brown sugar, butter and 1 teaspoon vanilla. Microwave on HIGH for 1 to 2 minutes until melted. Stir to combine well and pour into a 13 x 9-inch baking dish. Place pan in preheated oven so sugar mixture will completely melt and will spread evenly. Remove pan from oven and distribute sugar mixture evenly over bottom of pan. Place pineapple slices decoratively in pan, add cherries into centers of slices and then spread chopped nuts around the pineapple slices.
Meanwhile, place reserved pineapple juice in a 2 cup measuring cup and add enough milk to equal 1 1/3 cups. In a mixer bowl, combine cake mix, juice/milk liquids, eggs, and 2 teaspoons vanilla and beat for 2 minutes until light and fluffy. Pour batter over pineapple slices and even out batter. Place in preheated 350 degree oven and bake for approximately 35 minutes, or until center is set.
Remove from oven and allow to cool on wire rack for 3 minutes. Loosen cake from edges of pan with a knife and invert onto your serving dish so that the cake is upside down. Rearrange cherries and/or pineapple slices as needed and let cool completely. Makes 8 to 12 servings. Enjoy!