In a bowl rub together the sugar, flour, baking powder and butter until it resembles breadcrumbs. Add the oats, mix through the crumb mixture.
Line a baking sheet with baking paper, pour the mix onto the sheet and bake in the oven for 20 minutes.
Cut the rhubarb into 5cm (2in) lengths, place in a large pan with 50ml of water, cover, bring to the boil and then reduce to a gentle simmer for 7 minutes, until the rhubarb is soft. Remove from the heat and drizzle in the runny honey. Stir gently, replace lid and let stand for 5 minutes.
Spoon rhubarb into 6 serving glasses, break the crumble topping and sprinkle over the top of the rhubarb. Add a drizzle of honey and a spoonful of crème fraîche.