1Top and tail the gooseberries with a small sharp knife (if you've never done this before it means cut off the stalk and 'tail' bit).
2Put the flour, ground almonds, salt and vegan butter in a food processor. Pulse until the mixture resembles large breadcrumbs but stop before it clumps together. If you don't have a food processor, rub the butter into the flour and almonds with your fingers in a large mixing bowl.
3Preheat the oven to 175°C/350°F. Add the oats to the food processor and pulse a couple times. If you're not using the buckwheat, add 35g/1oz/⅓ cup more oats and pulse once more.
4Transfer the mixture to a large mixing bowl and stir in the sugar and the buckwheat if using. The mixture shouldn't stick to your hands too much. If it does, add more flour or ground almonds.
5Put all the gooseberries in a 28cm/11" long by 22cm/9" wide by 5cm/2" deep oven-proof baking dish and sprinkle over the sugar. You could use a deeper, less wide/long dish if you like.
6Spread the crumble mix evenly on top of the gooseberries and pat it down gently. Don't worry if it heaps above the top of the baking dish - the gooseberries will shrink down in the oven. If it does heap above the rim, put a baking tray on the oven shelf in case any juices spill over.
7Bake the crumble for about 45-50 minutes until golden brown. Check after 20, 30 and 40 minutes to make sure it's not burning. If it is, cover with aluminium foil.
8Remove from the oven and allow to cool for at least 20 minutes. Serve in bowls or on small plates. I like to eat this with vegan ice cream or vegan custard.