In a large bowl or in the bowl of a stand mixer (I only ever use a Bosch, never tried this in a Kitchenaid), mix the buttermilk, 3 cups flour and yeast together. Cover and let stand at room temperature until puffy and bubbly, 2-3 hours.
Add the sugar, eggs, salt, oil, and baking soda. Mix well and start adding the remaining flour until a soft dough is formed that clears the sides of the bowl and is smooth without being overly sticky or overflowed. Knead for about 7 minutes.
At this point, you can roll out the dough or cover and refrigerate for up to seven days. If doing so, place the dough in a large container or bowl as it will expand a bit in the refrigerator.
To use immediately, shape the dough into rolls: cloverleaf (three balls each about 3/4-inch in diameter popped into a greased muffin tin), crescent (divide the dough into thirds and roll each section into a 10- or 11-inch circle, brush with butter and cut into 8 or 12 sections and roll up), classic dinner rolls (about 2-3 ounces of dough rolled into a taut ball and placed in a 9X13-inch baking dish or on a large baking sheet). Cover the rolls with greased plastic wrap and let rise until double, about an hour or so.
Bake at 375 degrees until golden and baked through (exact time will depend on shape; for cloverleaf about 11 minutes, crescent about 15-16 and dinner rolls about 16 or so).
For refrigerated dough, pinch off the desired amount and shape. If the dough is really cold and hard to work with, let it rest covered at room temp for 30-45 minutes before shaping.
Once shaped, cover with greased plastic wrap and let rolls rise until double in size, 2-3 hours (dough taken from the refrigerator will take longer to rise since it's been chilled) and bake with the above instructions based on shape.
Remove from the oven and butter the tops, if desired.
Notes
Buttermilk: I usually don't plan ahead and get the buttermilk out of the refrigerator to come to room temperature so I pour it into a liquid measure and microwave it for 45 seconds (all microwaves will vary a bit) and then give it a good stir to get rid of any warm spots. Here is a guide for making your own buttermilk. Measuring the Flour: as with all yeast doughs, I never use the flour amount called for in the recipe as a hard fast rule (unless a weight measure is given and then I pull out my kitchen scale). Because humidity, temperature, altitude and a multitude of other factors can impact how much flour you need in your yeast doughs, I always judge when to quit adding flour by the texture and look and feel of the dough rather than how much flour I’ve added compared to the recipe. Tutorial: this tutorial on yeast may help identify how a perfectly floured dough should be.