Preheat the oven to 450 F / 230 C
Combine the vinegar with the plant milk, chill in the fridge.
Next combine the flour, baking powder, salt, and sugar in a bowl.
Grate the frozen butter (I recommend freezing it overnight, but 3 - 4 hours should work too) with the big holes of a box grater. Then stir the grated butter into the dry mixture with a fork.
By this time, the vegan buttermilk should be thick and curdled. Pour it into a bowl, and then dump the dry mixture on top. Even though this dirties another bowl, it makes it much easier to mix as you won't have any dry flour at the bottom of the bowl.
Dump out the dough onto a lightly flour surface. It may be crumbly, that's okay. Shape it into a rough rectangle.Roll it out to around an inch thick. Then fold it into thirds like an envelope. Turn it 90 degrees, and repeat this process 4 more times. This is what's gonna give the biscuits some flakey layers! If the dough is sticking to the rolling pin, just lightly flour the dough and pin as needed.Alternatively to folding, you can also cut the dough in thirds and then stack it. I personally find this easier so that's what I like to do. After you have rolled and folded the dough 5 times, roll it out to about 3/4 - 1" thick. You should be able to roll it to a 6x9 inch rectangle. Using a 3 inch cookie cutter, cut out 6 biscuits.Make sure you flour the cookie cutter so it doesn't stick. And very importantly, DO NOT twist the cookie cutter as this can seal the biscuit and keep it from rising. Reroll the scraps (you should get another 2 biscuits) You can also cut these into squares to avoid having scraps in the first place too!
Next add the biscuits to a parchment lined baking sheet. Make sure they are close to each other and snuggling and up against the lip of the baking sheet. This will promote a good rise.
Bake them in an oven at 450 F / 230 C for 15 minutes. Then pull them out, and brush them with some melted vegan butter. Add them back to the oven for 5 more minutes.
If the tops aren't as browned as you'd like at this point, you can throw them under a broiler, but keep an eye on them! They will burn fast. Once browned to perfection you can brush them with more vegan butter if you're a heathen like me!