Preheat the oven to 325°F. Generously grease a 10 to 12 cup bundt pan with butter or nonstick spray, then dust the inside lightly with flour, shaking out any excess.

In a medium bowl, whisk together the flour and baking powder until well combined, then set aside.

In a stand mixer fitted with the paddle attachment, beat the softened butter, softened cream cheese, and milk on high speed until smooth and creamy, about 2 minutes.

Add the granular sugar substitute to the mixer bowl and beat on high speed until the mixture is pale and fluffy, 4 to 5 minutes. Scrape down the sides of the bowl as needed.

Add the vanilla bean paste and mix to combine, then add the eggs two at a time, beating on medium speed just until incorporated after each addition.

Reduce the mixer speed to low. Gradually add the flour mixture, mixing just until no dry streaks remain. Do not overmix.

Scrape the batter into the prepared bundt pan and smooth the top with a spatula. Tap the pan firmly on the counter 2 to 3 times to help release any large air bubbles and level the batter.

Bake for 75 to 80 minutes, or until the top is deeply golden and a toothpick inserted into the center comes out with a few moist crumbs but no wet batter.

Transfer the pan to a wire rack and let the cake cool in the pan for 15 to 20 minutes, then carefully invert the cake onto the rack and lift off the pan. Let cool completely before slicing and serving.