Rhubarb - I used bright pink rhubarb as it looks pretty, but all rhubarb has the same tangy taste, so if yours is green it still works! I tossed it in 2 tbsp of flour right before adding it into the muffin batter to help prevent it from sinking to the bottom.
Buttermilk - You can use store-bought buttermilk, but I always make mine at home. Combine 1 cup of milk (dairy or non-dairy) with 2 tbsp of lemon juice. Allow it to sit on your counter for 10-15 minutes to activate before using.
Temperature - The muffins go into the oven at 425F, but as soon as they are in the oven, decrease the temperature to 375F! Doing an initial hot temperature gives the levening agents a boost to lift and create that perfect muffin dome. Then the lower temperature helps the muffins continue to bake.
This recipe makes 12-14 muffins, depending on how full you fill each liner. I made 12 muffins!