Step 1

Heat the oven to 170°C/150°C Fan/325°F. Line a 23cm / 9-in square tin with a sheet of baking parchment, so that it covers the bottom and comes up the sides of the tin. Leave something heavy on it to keep it down while you melt everything together.

Step 2

Measure the oil in a jug, and pour it into a fairly wide, heavy-based saucepan; I use one of 22cm / 9in diameter. Measure the syrup and treacle using the oily jug, as this will stop them sticking and help them pour out easily into the saucepan.

Step 3

Tip the sugar into the pan, and chop the prunes finely before adding them. Peel the ginger with the tip of a teaspoon and grate it finely into the pan. Sprinkle in the spices and salt and warm over gentle heat, whisking to combine. But don’t whisk too much: you do not want to get a lot of air in the mixture.

Step 4

Once everything’s melted and mixed, take the pan off the heat; it should be warm at this stage, rather than boiling hot. Add the oat milk, whisking gently to make sure it’s incorporated.

Step 5

Whisk in the flour in 3 or 4 batches, getting rid of any lumps patiently as you go. This will take a few minutes; the only lumps you should see are the little bits of prune, although they will melt into the gingerbread as it bakes.

Step 6

Dissolve the bicarb in the warm water in a bigger cup than you think it needs, then add the vinegar and quickly whisk the fizzing mixture into the pan.

Step 7

Pour the gingerbread batter into the lined tin carefully and bake for 50–55 minutes, though start checking at 45. It may look cooked at 45 minutes, but as it’s so damp, a cake tester won’t help enormously – you’d expect some crumbs to stick to it – so take it out of the oven and touch the top quickly; if cooked, it should bounce back a bit under your fingers.

Step 8

Leave to cool in its tin on a rack, although I’m afraid I’m going to caution you against eating it the minute it’s cold. To taste this at its best, wrap the tin first in baking parchment and then in foil, and leave for a day or two before cutting into it.