Preheat the oven to 190C/375F and line a baking tray with grease proof paper.
Place the flour, sugar, bicarbonate of soda and salt into a large bowl. Add in the cubes of butter an either use a pastry cutter or your hands to cut the butter into the flour mixture. Continue until you have a coarse breadcrumb texture.
Add in the raisins and stir briefly to disperse.
Add in the egg and buttermilk. Begin to bring the mixture together by stirring gently. You want the dough to come together into one lump with no flour left in the bowl. The dough should be a little sticky, but not so wet and sticky it's a gloopy mess.
If the mixture is too wet, add flour 1tbsp at a time and mix. If it is too dry, add a little more buttermilk, 1tbsp at a time. The amounts above made the perfect consistency dough for me, but everyone's scales are calibrated differently and there are many other things that can affect dough! Just be careful and add things little by little.
Tip the dough into the centre of your baking tray. Flour your hands lightly and then gently shape the dough into a circle around 7 inches across. Take a serrated knife and score the dough left to right and up to down to make a cross.
Place the bread into the oven for 35-40 minutes, until risen, golden all over and an inserted knife into the centre comes out clean, with no wet dough. The bread should have a good golden colour all over.
Leave to cool for at least 30 minutes before digging in. Irish Soda Bread can be served warm from the oven, toasted or at room temperature and is great with butter and/or jam. It will keep in a Ziploc bag, at room temperature for 6-7 days.