Preheat the oven to 450F. If you have a baking stone, put that on a rack to preheat too.
Mix the flour, salt and baking powder together.
Add the buttermilk and stir together. The dough should be slightly soft but not too sticky or wet.
Turn onto a floured surface (board or counter) and knead a few times. If it's too wet (as mine was because I didn't think about the fact that I added 2 Tbs lemon juice to the liquid really ), add some more flour and knead it in.
Shape the dough into a rough circle by folding the top over and under, then pat down until it's about 1 1/2" high.
Put the dough onto the preheated stone or onto a baking sheet.
Slash a plus sign + into the dough, all the way to the edges. The cuts help the bread rise.
Bake at 450 F for 15 minutes, then lower the heat to 400F and bake another 30 minutes.
You can test to be sure it's cooked through by tapping on the bottom and listening for a hollow sound.
Cool a bit on a wire rack and then slice.