Preheat the oven to 350F.
In a large bowl mix together the water, sweet potato, eggs, 1 Tablespoon of vanilla, and pumpkin pie spice until well combined. Add the cake mix and baking soda, mix until just combined.
Grease a 9×13 pan with butter and pour batter into pan.
In a small bowl mix together 1/2 cup of brown sugar, 1/2 cup flour and melted butter. Use your fingers to sprinkle over the top of the cake. Bake at 350 for 25-30 minutes, or until a toothpick inserted comes out clean.
For the glaze, combine the other 1/2 cup brown sugar, granulated sugar, 1 teaspoon vanilla, and heavy cream in a saucepan and bring to a simmer. Remove from heat and stir until all sugar is dissolved.
When cake is finished baking, poke holes in the top with a toothpick. Pour glaze over the cake, making sure to cover all surfaces. Serve cake warm or at room temperature.