In a large bowl, combine the yeast and 1 teaspoon caster sugar in ½ cup (150 ml) warm milk.
Cut out 18 x 4-inch (10 cm) circles of parchment paper.
Spread the dough to a thickness of about ½ inch (1,25 cm).
Cut 2-inch (5 cm) circles with a cookie cutter and place the circles, spaced, each on a circle of floured parchment paper.
Add about 6 cups of oil into a medium-sized deep frying pan and heat to a temperature of 350 F (170 C).
Using the parchment paper, slide each circle of dough into the hot oil and fry the donuts on both sides while maintaining the oil at a temperature of 350 F (170 C) until they are golden brown.
Generously sprinkle caster sugar (or icing sugar) onto the donuts.
The donuts can be served nature or filled. In addition to jam, the donuts can be garnished with vanilla custard or chocolate spread.
They can also be covered with chocolate icing as well as sprinkles.
There are two ways to fill the donuts. By cutting them in half or by using a syringe to inject the filling.