If using active dry yeast, heat the milk in the microwave or on the stovetop until it is “fingervarm” (finger warm), meaning it should feel warm to the touch but not hot. Add your yeast, stir, and leave it for 5-10 minutes until the mixture starts to bubble up. If using instant yeast, simply add the yeast to the milk - there is no need to dissolve it.
Combine the sugar, egg, and egg yolks in a large bowl. Once the yeast mixture has bubbled up a bit, add it to the egg mixture, or if using instant yeast, add immediately. Mix well.
Then, add the salt, flour, and softened butter, and mix with a wooden spoon until the dough starts to come together. Tip it out onto a floured surface and knead until smooth and elastic (about 10 minutes). Add more flour if needed - the dough should be soft and smooth, not dry and not sticking to the surface. If using a stand mixer, allow it to knead the dough together for about 10 minutes. Make sure the dough doesn't stick to the sides of the bowl in the mixer!
During the final 2 minutes of kneading, add the raisins to the dough.
Make sure the raisins are evenly distributed in the dough. If you knead with the mixer, you may have to knead it a few times by hand to get them to mix in properly.
Cover the dough with cling film or a clean dishtowel and place in the fridge overnight for 8 hours, or let rise at room temperature (if room temp is very cold wherever you are, put it in a warm place, i.e. under a light) for 1-1.5 hours or until doubled in size.
Once your dough has doubled in size, divide into 12 equal sized balls.
To shape the rolls properly, you should first divide your dough into equal sections. Take a piece, pinch together into a ball shape, then cup it in your hand with the top of the roll touching your palm. Place your hand on an unfloured surface with the seam of the roll touching the table. Move your cupped hand in quick, tight circles - this will cause the seam to come together and create tension on the surface of the dough, meaning it will rise upwards in the oven, instead of flattening.
You should be left with a perfectly round dough ball!
Place the rolls on a parchment lined baking sheet. We like to place them closer together so they can touch and rise upwards as they bake.
Cover and let the rolls rise for another 30-45 minutes. In the meantime, preheat your oven to 400 degrees F (204 degrees C). To check if they are ready, use the poke test. Poke the dough with one finger. If the dough springs back immediately, it needs more time. If it springs back slightly but an indentation remains, it's ready to be baked.
Brush the buns with egg wash (whisk together one egg and some water until there are no more gloopy egg streaks).
Bake for 10-12 minutes. Check the bottom of the buns to see whether they are done – they should be golden brown. If they’re too pale, they’ll need another minute or two.
Enjoy warm with butter and jam (or anything you like!), or on their own as a snack!