Pre-heat the oven to 170°c
Place your muffin cases in a 12 hole muffin tin
Get 2 small bowls and one large mixing bowl
Place the butter in a small bowl and melt in the microwave for a few seconds, set aside to cool.
In the 2nd small bowl, add the brown sugar to the chopped rhubarb. Stir until all the Rhubarb is covered and set aside
In the large mixing bowl, Sieve the flour, bicarbonate of soda, baking powder,cinnamon and salt (*Only if your using unsalted butter) together, mix until combined.
In the Butter bowl: Add your eggs, yogurt, and vanilla extract. Beat together until combined. Add the mashed bananas and stir well.
In the large mixing bowl: Make a well in the middle of your flour mixture and pour in the egg/banana mixture. Fold in until gently combined.
Lastly add the Rhubarb/sugar mix and fold in until completely combined.
Fill your muffin cases to the top and sprinkle some dark brown sugar on top.
Give the muffin tray a little wiggle to even out the cake batter
Bake in the bottom of the oven for 20-25 minutes until a skewer comes out clean
Place on a rack to cool . Serve warm or cold!