Heat oven to 220C/200C fan/gas 7.
Line a 12-hole muffin tin with paper
muffin cases. Stir the sugar and rhubarb
together and set aside while you make
the crumble topping. Mix together the
muscovado sugar with the flour, oats
and cinnamon, then rub in the butter
until clumpy with your fingertips.
Quickly spoon into the cases, then
scatter each with a thick layer of the
crumble mixture. Bake for 15-18 mins
until golden and a cocktail stick poked
into the centre of a muffin comes
out clean. Cool on a wire rack.