Preheat the oven to 350F.
In a large bowl, whisk together flour, baking powder, baking soda, and salt.
In a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, beat butter and cream cheese until smooth. Add sugar and beat at medium speed until light and fluffy, about 5 minutes.
Add 3 eggs, one at a time, beating until each is fully incorporated before adding another one. After adding 3 eggs, add 3 tablespoons of the flour mixture. Continue adding the other 3 eggs, one at a time. Beat in the vanilla.
Add ⅓ of the flour mixture mixing at low speed until combined. Add half of the milk and mix until combined. Repeat, alternating with the rest of the flour mixture and milk.
Butter and flour a 12-cup Bundt pan or spray with baking spray with flour.
Pour the cake batter into the pan and tap gently on the counter a few times to settle the batter.
Bake for 45 minutes or until golden brown and a toothpick inserted into the center comes out clean.
Let cool in the pan for 20 minutes. Invert onto a cooling rack and cool completely.
In a small bowl, whisk together the powdered sugar, milk, and vanilla until smooth. Pour over the cooled cake.
