Gluten Free Rhubarb and Custard Crumble Shortbread Slice - Coeliac Sanctuary

https://www.coeliacsanctuary.co.uk/recipe/gluten-free-rhubarb-and-custard-crumble-shortbread-slice

Posted On: 11th July 2026

Looking for a gluten free rhubarb recipe? This gluten free rhubarb and custard crumble shortbread slice features a buttery shortbread base, thick custard filling and fresh rhubarb beneath a crisp gluten free crumble topping.

Ingredients

350g gluten free plain flour
100g caster sugar
200g margarine
500ml milk
60g custard powder (I used Bird's tub)
50g sugar
100g rhubarb

Preparation Time: 15 Mins
Cooking Time: 45 Mins

This recipe contains

Dairy

Method

1. In a bowl place the gluten free plain flour, sugar and margarine. Begin by rubbing the margarine into the gluten free flour to spread it evenly through the mix, then bring together with your hands and work into a dough. Split 1/3 of the dough off and set aside for the crumble topping.

2. Grease and line a 9in square baking tin and press the gluten free shortbread dough into the bottom of the tin. Using baking paper will help you lift it out once everything is cooked and set later.

3. Place the gluten free shortbread in an oven preheated to gas mark 4/180c and bake for 15 mins until firm and very slightly browned.

4. Meanwhile, make your custard up. Place all but about 50ml of the milk into a saucepan and heat until warm. Leave the remaining milk in a jug.

5. Mix the sugar and custard powder into the remaining 50ml of milk then pour into your pan of warm milk. Keep it on the heat and keep stirring as you pour. Keep stirring until your custard goes super thick, don't stop otherwise it will go lumpy.

6. Thinly slice your rhubarb, this is going to go on top of your custard. I used a mandolin to make sure they were nice and thin and evenly sized.

7. Once your gluten free shortbread is out of the oven, pour the custard on top of your shortbread, scatter the thin rhubarb slices on top then break up your remaining shortbread mix, crumble it between your fingers onto the top of the rhubarb and custard to make a chunky gluten free crumble.

8. Return you bake to the oven and cook for a further 30-35 mins on gas mark 4/180c, the crumble on top will be lightly brown and the rhubarb softened.

9. Leave your gluten free shortbread slice to go completely cold, I recommend refrigerating for at least 6 hours to make sure custard is completely set and chilled through then enjoy!

This recipe makes 12
Nutritional info per slice