Oh I do like soda bread, occasionally I'll risk the treat of frying slices of it in butter, but it is best warm from the oven, so best get making it then.
You sift the flours, soda & salt into a large bowl, mix them and make a well. Pour melted butter, treacle & buttermilk into the well & bring together to make a dough. It doesn't need much work. Bring that to a ball & flatten it out then make a cross in the top. The handle of a spoon works well for this. Dust lightly with a bit more flour and then put into a hot oven.
You can tell its done when the dough visible in the cross is dry or when the loaf makes a hollow sound. Let it stand for about 5-10 minutes (this is necessary if you are using a knife, if you are just going to rip it open, then as soon as your fingers can handle it)
It doesn't really need anything more than butter, but it does have to be butter, margarine & spread just won't do. Eat and enjoy. Soda bread doesn't keep (apparently), but stopping eating it is more of a challenge than not. Should you have some a day or two old. Slice it, melt an unhealthy amount of butter in your frying pan & then toss the slices in till browned on each side. Deny all knowledge of this to any passing Dr or Nutritionist.