Preheat the oven to 425°F. Line a baking sheet with parchment paper then set aside.
In a measuring cup, combine non-dairy milk and vinegar. Whisk together then set aside.
In a large bowl, whisk together spelt flour, all-purpose flour, baking powder, baking soda and salt. Add margarine and cut it roughly into flour using a pastry cutter, until mixture is the texture of coarse meal. Work quickly so the margarine does not melt. Add milk/vinegar and stir with a wooden spoon until just combined. Careful not to overwork.
Lightly flour the parchment paper then transfer the dough on top. Using your hands, pat into an oblong shape, about 1 inch thick. Using a lightly floured cookie or biscuit cutter, cut the biscuits out and place them on a baking sheet. Brush the tops lightly with melted butter. Bake for about 12 to 15 minutes, or until they begin to turn golden. Remove biscuits from oven immediately and transfer to a wire rack to cool.