To make topping combine brown sugar, butter and cinnamon until crumbly, set aside. To make muffins, cream together brown sugar, butter, egg, vanilla and almond extract until light and fluffy. In separate bowl, stir together flour, baking powder and baking soda. Add to sugar mixture alternately with buttermilk, stirring just until dry ingredients are moistened. Do not overmix. Batter should be lumpy and tends to be thick. Fold in Rhubarb. Divide among dozen large muffin cups (paper-lined), filling until full. Sprinkle each generously with topping mixture. Bake in a 190ºC oven for 25 to 30 minutes or until a toothpick inserted in the centre comes out clean.