40gvegan margarine or vegan butterabout 2–3 tablespoons
2teaspoonsfinely grated lemon zestfrom about one medium lemon
Water – just enough to bring the total liquid (rhubarb juice + water) to 500 ml / 2 cups; this depends on how much juice the rhubarb releases after sitting with the sugar
Streusel Topping
160gflourI used type 630 spelt flour, but any light wheat or spelt flour works well
Prep the rhubarb.Wash the rhubarb, trim the ends, and slice it into small pieces — no need to peel it. Toss the pieces with the sugar and let them sit for 2–3 hours in the fridge. This draws out a lot of liquid, which we’ll use for the pudding layer.
Preheat your oven to 200°C (390°F), top and bottom heat.
Line the bottom of a round 26 cm (10-inch) springform pan with parchment paper.
Make the crust.Mix the crust ingredients together — it doesn’t have to be perfect; the dough can be a bit crumbly. Press it into the pan using your fingers and the back of a spoon, making sure to push it up along the sides to form a high edge. It might feel a bit fiddly, but it’s easy and only takes a few minutes.Place the pan in the fridge while you prepare the pudding and the streusel.
Make the pudding filling.Pour off the liquid from the rhubarb and weigh or measure it. Add enough water to bring it to 500 ml (about 2 cups) total.💡 If your rhubarb is super juicy, you may already have enough liquid and won’t need to add any water.In a small saucepan, whisk the liquid with the starch, sugar, vanilla powder, lemon zest, and margarine. Bring to a gentle boil, whisking constantly, just like a pudding. Once it thickens, remove it from the heat and stir in the rhubarb pieces.
Make the streusel.In a bowl, mix together the flour, sugar, vanilla, and soft margarine (or vegan butter). Use your hands to form chunky crumbs.
Assemble.Pour the rhubarb pudding into the prepared crust and smooth it out.Take portions of the streusel dough, squeeze it gently in your hand to form clusters, and sprinkle them over the pudding in whatever size and shape you like.
Bake.Bake the cake on the lower rack of the oven for about 1 hour, or until the streusel is nicely golden-brown.Check around the halfway mark — if the streusel is browning too quickly, loosely cover the cake with foil.
Cool completely.Let the cake cool completely before slicing — otherwise, the filling may still be too soft.
Serve.Dust with powdered sugar before serving. Enjoy!