Preheat oven at 350 F.
Grease a 12-cup bundt pan with cooking spray.
Beat butter in mixing bowl until smooth and creamy. Add sugar and beat another 2-3 minutes until light and fluffy.
Add first 2 eggs one at a time then mix. Wait till the egg is absorb into the mixture
Add 2 more eggs then beat again in a medium setting.
Add vanilla and ube extract then continue beating until fully mixed in.
Combine flour, cornstarch, baking powder and salt in separate mixing bowl.
Add half of dry ingredients into wet ingredients. Add milk then mix until combined.
Add remaining dry ingredients and stir until just combined.
Transfer the mixture to a greased Bundt pan.
Bake at 350 F for 35-45 minutes or until toothpick inserted comes out clean.
Let it cool in a pan for 10 minutes, then invert onto a cooling rack to cool completely.
Make glaze: Whisk together powdered sugar, milk, vanilla, and salt. Pour over cake and serve.