Pre-heat oven to 350 degrees. Grease a 9x13 cake pan.
If you have a stand mixer-fit with paddle beater. Beat on high speed the butter and until light and fluffy.
Add in sugar. Beat until the mixture is light and fluffy, about 2 minutes.
Scrape down the sides and turn your mixer to low. Add in the egg, sour cream, and vanilla and mix to combine.
Scrape down the sides. As the mixer is running on low speed add in the baking soda. Slowly add the flour a 1/2 cup at a time and mix to combine. Final dough will be soft.
Press into the bottom of a greased 9x13 cake pan. The dough will be sticky. It's ok.
Bake at 350 degrees for 20-25 minutes or until a toothpick comes out clean.
Cool on a cooling rack completely then frost as desired. My preference for these is frosting with buttercream or cream cheese buttercream