Preheat the oven to 220C/Gas 7/fan oven 200C.
Combine all the spices and salt in a small, electric
spice or coffee grinder (or use a pestle and
mortar), and pulverise them to a powder – ignore
the bigger bits of coriander husk. Tip the ground
spices into a very large mixing bowl.
Cut the onions into sixths, leaving a little root
attached to hold the layers together. Cut the
ordinary potatoes into six segments, lengthways.
If the sweet potatoes are slender (they normally
are) cut them into quarters, lengthways; if they’re
bulky round the middle, cut them into sixths. Put
all the vegetables into the mixing bowl, add the
oil and toss thoroughly, using clean hands
Lightly oil the large tray which comes with your
oven (or 1 or 2 baking trays), spread the
vegetables out in a single layer and bake them
for 25 minutes. Meanwhile, combine the glaze
ingredients in a small jug with 4 tablespoons
cold water. Remove the oven tray, brush the
vegetables with the glaze and continue to bake
for about 20-30 minutes, or until they’re slightly
charred and tender. A little squeeze of lime or
lemon juice adds vivacity, but the vegetables are
very nice with or without it.