Preheat your oven to 325°F (160°C). Prepare a 10-inch Bundt pan by thoroughly greasing and dusting it with flour. This prevents sticking.
In a large bowl, beat the softened butter and granulated sugar until light and fluffy. This usually takes about 3-5 minutes.
Add the eggs one at a time, beating well after each addition. Ensure each egg is fully incorporated before adding the next.
Stir in the cultured dairy product and vanilla extract. Mix until just combined. Do not overmix this mixture.
In a separate bowl, whisk together the sifted flours and baking soda. Gradually add these dry ingredients to the wet mixture. Mix on low speed until just combined. Avoid overmixing the batter.
Pour the batter evenly into your prepared Bundt pan. Bake for 60-75 minutes. The top should be golden brown.
Test for doneness by inserting a wooden skewer into the center. It should come out clean.
Let the cake cool in the pan for 10-15 minutes. Then, invert it onto a wire rack to cool completely.