For our muffins we needed a cup and a half of flour, half a teaspoon each of baking soda and salt, three-quarters cup of brown sugar, half a cup of buttermilk — or use sour milk, or milk mixed with a half-tablespoon of lemon juice — three-quarters cup of vegetable oil, an egg, a teaspoon of vanilla, and half a cup of chopped nuts.
To this we added the last of our rhubarb, one cup's worth chopped.
We're going to use a topping made from a quarter cup each of brown sugar, chopped nuts, and oats, and a half-teaspoon of cinnamon.
After preheating the oven to 325 and greasing up the muffin pan (we use a 6 large pan, but a 12 small works too), we combined the flour, soda, and salt, then added brown sugar, buttermilk, oil, egg, and vanilla. This was mixed together until it was moist, and then we stirred in the rhubarb and nuts.
The batter was scooped into the tray, and then sprinkled with the topping we prepared earlier. After about half-an-hour our muffins were done.