Pour lukewarm water into a small bowl and sprinkle the yeast over. Stand for about 5 minutes. Combine the butter, caster sugar and salt in a large bowl. Pour the boiling water over and stir in the evaporated milk. Cool to lukewarm and then add the yeast mixture with the eggs. Mix well.
Slowly mix in the flour until the dough forms a ball. Cover with plastic wrap and refrigerate for 30 minutes to 1 hour.
Working with a small portion (a little larger than a tennis ball) at a time, roll out the dough to 3mm thick. Cut into strips about 5cm wide, then cut again in the opposite direction and at an angle, making diamond shapes.
Heat oil in a deep and wide saucepan over medium-high heat to 180 degrees C.
Slide dough slowly into the oil to avoid splattering and deep fry until they puff up and are golden brown, 3 to 5 minutes. Carefully remove onto a rack covered with paper towels. Allow to cool until they are cool enough to handle. Place in a clean paper bag with icing sugar and shake gently until covered generously or, use a sifter to dust the beignets with icing sugar.