Preheat oven to 400 degrees F (204 C) and set out a baking sheet.
In a liquid measuring cup (or small bowl), combine dairy-free milk and lemon juice or apple cider vinegar and stir to combine. Set aside.
To a large mixing bowl, add gluten-free flour blend, almond flour, cornstarch, sea salt, baking powder, and baking soda and whisk to combine.
Add vegan butter (or coconut oil) and use a pastry cutter, whisk, or fork to "cut" the oil into the flour until small bits remain (see photo).
Add 3/4 of the vegan buttermilk to the dry mixture and stir with a spoon to combine. You're looking for a semi-sticky dough, and you may not use all of the buttermilk. I used all but 1-2 Tbsp (as original recipe is written // adjust if altering batch size). If it looks too wet, compensate with 1-2 Tbsp at a time of almond flour or gluten-free flour blend.
Transfer your dough onto a well (gluten-free) floured surface and dust the top with a little gluten-free flour. Handling as little as possible, form into a 1-inch-thick disc with your hands (these biscuits don’t puff up as much as their gluten-containing cousins, so only push the dough down as much as you desire them to be thick).
Then, using a well-floured biscuit cutter, small cookie cutter, or narrow drinking glass, cut out biscuits and transfer carefully to a baking sheet with a spatula. Arrange the biscuits so they are close but not touching - see photo).
Continue, reforming dough as needed, until all of the dough is used (as the recipe is written, about 10-12 small biscuits or 6-8 medium biscuits). Brush the tops of the biscuits with melted vegan butter.
Bake for 15-20 minutes or until they look dry and slightly fluffy. Then increase heat to 450 F (232 C) and bake for another 2-4 minutes to brown the outside (see photo). Watch carefully and be sure not to burn.
Remove biscuits from oven and let rest on pan for 10 minutes. Then transfer to a serving plate to cool completely. It's important to let these cool and the steam to release or they can be a bit on the moist side. Warm or room temperature is best for serving.
Best when fresh. Store leftover biscuits covered at room temperature for 3 days or in the freezer up to 1 month. These would go well with vegan gravy, and are especially delicious with a little vegan butter and jam or compote!