Whisk the yeast, milk, and one teaspoon of the sugar together in a bowl and leave until frothy (about five minutes).
Put half of the flour into a separate mixing bowl and make a well in the center. Slowly pour in the milk-yeast mixture and stir with a fork to form a shaggy dough. Cover the bowl with plastic wrap or a damp cloth and leave in a warm spot for about an hour, or until the dough has doubled in size.
When the dough has doubled, punch down to deflate. Add the eggs to the dough and use a fork or your hands to combine. Do the same thing with the sugar, and then the remaining flour. Knead for around 5 minutes and form a ball. Cover again and leave to prove for 30-45 minutes in a warm place.
When ready, lightly flour a large board or another workspace. Use a rolling pin to roll out the dough to about an 18-inch square. Working quickly, use a knife to spread the butter evenly over the dough.
Roll the dough up from the bottom of the square to the top, and slice into rounds that are about 1-inch thick. Transfer to a plate.
Lightly re-flour your workbench. Using your hands, roll out each individual round of dough into a long rope shape. Then shape each rope into the traditional snail-shell coil of the ensaimada.
Line baking trays with parchment paper, and put the ensaimadas on top (leave plenty of space as the pastry will expand). Leave to rise until dough has doubled again in size (at least 3-8 hours, you can leave overnight).
When ready to bake, preheat your oven to 350F (180C). Bake for 12-15 minutes or until golden brown on top. Leave to cool for at least 20 mins, and then dust with powdered sugar.