I've written about Irish soda bread before, but now I've gotten the recipe perfected.
Start oven preheating to 425°F. Mix vinegar and milk in glass, and leave it to sour for at least 5 minutes. Place some parchment paper onto a cookie sheet. In a large bowl sieve and combine all the dry ingredients, mixing thoroughly. Pour in soured milk and mix together. Briefly knead dough into a ball and place on parchment paper on cookie sheet. Cut cross into top of bread, cover with large metal bowl, and put in oven. After 30 minutes, remove metal bowl. Bake for 10 to 15 minutes longer, until done.
Bread is done when browned and top is firm. You can double-check doneness by thumping on the bottom of the loaf, it should sound hollow. Place bread on rack to cool.
Dough should be sticky. You can use buttermilk, I use milk soured with vinegar because I always have milk around, and never have buttermilk around.
This is a really fast and easy bread.
I leave it on the cutting board, with the cut side down, that helps it last a little longer without much fuss.
Don't knead it very much. It rises from the reaction between the lactic acid in the milk and the baking soda. If you knead it too much, you'll lose a lot of the gas.
Because it's chemically leavened, you can use all sorts of flours. So far, my two favorite variations are 100% white all-purpose flour, and 50% all-purpose, 25% whole wheat, and 25% amaranth.