Preheat oven to 185 degrees Celsius. Line muffin trays with paper liners or coat them with nonstick spray. Sift the flour, baking powder, soda and salt in a bowl and set aside.
Beat the unsalted butter and brown sugar with an electric mixer in a separate bowl until light, pale in colour and fluffy. Add in the egg and beat until incorporated. Add in the sour cream / yoghurt / buttermilk and coffee and beat it in. The mixture will look curdly and ugly.
Fold in the flour mixture in two batches – do so very, very, very gently as you do not want to lose all the air that you’ve beaten in just now. Fold until the flour just disappears – I managed to survive with some specks of flour here and there. (: Gently fold in the raisins and chocolate chips.
Using an ice-cream scoop or 1/4 measuring cup, scoop the batter into the paper liners or until they are 3/4 full. Bake for 25-30 minutes until the tops are golden and a skewer inserted to the middle of the muffin comes out clean.
Remove the muffins from the trays and let cool on a wire rack.