Preheat the oven to 180C/350F/Gas Mark 4.
Put softened vegan butter and caster sugar in a large bowl or bowl of your food processor and mix using wooden spoon/hand held mixer or paddle attachment of your standing mixer until pale in colour and fluffy.
Sieve in the flour, spices, baking powder and salt and continue mixing until dough starts coming together.
Add zest of an orange (if using) and currants or raisins and continue mixing.
Add just enough oat milk to bring the dough together (½-1 tablespoon) and take it out onto lightly floured counter.
Roll the dough out so that it’s roughly 5mm thick and using 6cm round, fluted cutter (or any cutter of your choice) cut out the biscuits, re-rolling the dough until it’s all used up.
Transfer biscuits to non-stick/lined baking trays and bake in preheated oven for 10 minutes.
While biscuits are baking prepare the glaze by mixing oat milk and agave syrup.
Take biscuits out of the oven and brush them gently with the glaze and sprinkle with some caster sugar to create a layer of sugary coating.
Return biscuits to the oven for another 5 minutes until light brown and fully baked.
Take them out of the oven and leave on the baking trays for a few minutes before you transfer them onto the cooling rack to cool completely.