1. Preheat the oven to 325 degrees Fahrenheit.
2. Spray mini loaf pans with nonstick cooking spray. You can also use an 8×8 square pan and line it with Gefen Parchment Paper for easier cake removal.
3. In bowl of standing mixer fitted with a paddle attachment, mix flour, sugar, baking soda, and salt on low speed to combine.
4. With mixer running at low speed, add margarine one piece at a time. Continue beating until mixture resembles moist crumbs.
5. Add egg, yolk, vanilla, and buttermilk; beat on medium- high speed until light and fluffy for about one minute.