Preheat the oven to 375 ℉. Prepare a 9 inch cast iron pan with baking spray or a large baking sheet with parchment paper.
In a small bowl or measuring cup, stir together milk and vinegar and let sit 5 minutes.
Add egg to milk mixture and whisk well.
In a mixing bowl combine flour, baking soda, salt, and butter. Crumble butter with hands or a fork into the flour mixture until it's in pea sized pieces.
Mince onions and chop cheese into small pieces, about ¼ inch cubes (about .5 cm).
Add the onions, cheese, and garlic to the flour mixture.
Pour the milk mixture into the dry ingredients and mix to form a dough.
Once the dough is formed, knead about 10 times, making sure that all flour pockets are gone. Gently form into a ball, use flour if you need to keep the dough from sticking to your hands.
Place the dough ball in cast iron frying pan (or prepared baking sheet) and cut a cross ¼ inch deep into the top of the loaf using a knife.
Bake for 45-55 min, until internal temperature of loaf is 200℉. Let cool for at least 30 minutes before slicing. Enjoy!
Notes
NOTE: 4 oz is the minimum amount of cheese. We enjoyed adding more! If you use garlic powder in place of fresh garlic, remember to use half the amount called for in the recipe. Store at room temperature for up to 3 days. Freeze for up to 3 months.