In a medium bowl, sift together the flour, baking powder, and salt. If you're using cheese, spices, herbs, or other add-ins, mix them in now.
Add the yogurt and milk bit by bit and mix gently until incorporated. You want to use a mixing technique that is similar to cutting in butter (the idea is to keep the dough crumbly, so your aim is not to make it one homogenous ball).
Turn the dough out onto a floured surface and gently knead it together. Do not overwork the dough! The best way is to fold it over and over onto itself and press down to work it together (like you would making puff pastry). Roll it into a flattened disc, about 2 inches high (you can size them to your liking -- I prefer higher, fluffier biscuits).
Using a biscuit cutter, punch out rounds until you have no dough left. Place them on a parchment lined baking sheet.
Sprinkle biscuits with coarse or flaky salt and bake for 12-15 minutes (start checking at 10 minutes). Take them out when they are just barely golden brown.