You can replace nigella seeds with cumin seeds.
It doesn't have to be added gradually. The recipe I use (a Nigella Lawson) involves adding it all at once.
Yes, you can substitute brandy instead of sherry in a cookie recipe.
Ian hines is the best recipe
Honey
MANyasie Veganaise
No.
sherry
If the recipe calls for coriander seeds, cumin and caraway seeds are good substitutes. If the leaves of coriander is what is required for the recipe, this is also known as cilantro. In this case, fresh parsley can be used as a substitute.
Tesco's
tapioca starch
You should follow what the recipe says.
I'd use honey instead.