It helps to understand the baking science behind successful biscuits.
1. Why use a soft wheat or other low protein flour? The lower the protein content the less gluten will build up during handling. Gluten is great for making bread but not for fluffy biscuits or scones or cakes. If you don’t have access to soft wheat flour you can lower the protein content of regular all purpose flour by subbing some cornstarch for equal parts of flour. I use a ratio of 1 tablespoon for 1 tablespoon of flour for each cup of flour.
2. Why sift the flour several times? Aerating the flour will help lighten it and make it easier to mix in the cold butter.
3. Why cold, very cold butter. Butter consists of water and fats. When your biscuit dough hits the hot oven the water in the butter becomes steam and helps lift the biscuit. A good butter such as Kerry Gold makes all the difference in taste and texture.
4. Why mix the liquid ingredient in quickly? See above about gluten. Even a low protein flour will develop gluten when liquid is added. So over mixing will give you a chewy biscuit.
5. Why be precise in your measurement of dry ingredients but not the butter or liquid? How flour behaves (for want of a better word) depends on a few variables. If working in a humid room the flour will absorb moisture and you may need to use less liquid. If in a very dry environment extra liquid may be called for. It also depends on if you want dough that will roll our or dough for drop biscuits or hand formed. This is where you can experiment to see what results you like best.
If it ends up looking too wet let the dough sit to hydrate for a few minutes. That usually does the trick. Don’t add more flour to the dough. Doing so will mean a tougher biscuits. Instead put extra (AP) flour for rolling it out. For drop biscuits put some flour on a plate and drop each scoop/spoon of dough into the flour. Toss the portion in the flour then shake off any excess before putting in the pan.
As for the butter you can use as little as two tablespoons up to a stick. Again find out what you like. As long as the amount you use is disbursed through the butter it will work.
PS. If using volume measurements for flour instead of weighing it how you measure out the flour is very important. Do not pack it into your measuring cup. Instead loosen the flour by stirring it with a fork then spoon or scoop it in, and then use a butter knife to level off any excess.