Soften the butter to room temperature, and place in a mixing bowl. Mix on low speed.
Whisk together the caster sugar and eggs, and add this mixture to the butter in the mixing bowl, while mixing on low speed.
In a separate bowl, mix together the flour, whole milk, and yeast.
After the caster sugar, eggs, and butter are mixed together, combine the second mixture into the mixing bowl while maintaining a low speed.
Once completely mixed, add the salt while keeping on low speed.
You should now have your dough forming. Knead the dough until smooth, and shape into a ball. Place in a bowl covered with foil.
Once dough is twice its volume, roll out at 1 cm thick, and cut donut shapes. Place these dough-donuts underneath a towel, and leave to sit for 30 mins at room temperature.
Pre-heat 1 kg of sunflower oil to 350°F.
Place your dough in the oil, and let fry. Prep wax paper on a tray, and place donuts on tray after fried.
Let donuts sit and cool in the fridge.