Whisk all ingredients together until smooth. Store in a clean, well-closed jar in the fridge for up to 3 days.
Notes
The thicker your buttermilk, the creamier your dressing will be. Modern buttermilks can actually highly vary in thickness – if yours is very liquid, consider using half buttermilk, half Greek yogurt for a creamy consistency.
Feel free to use fresh herbs in place of the dried, just double or triple the quantity the recipe calls for.
I highly recommend sticking to real buttermilk (or powdered buttermilk you rehydrated according to package directions) in this recipe, it's essential to the flavor of a classic Ranch dressing.