I love making doughnuts and this is a really good one. We love cajeta or dulce de leche in our family and this was a perfect combination. You will love these doughnuts you wont be able to eat just one. A favorite recipe in our family now.
In a mixing bowl add warm water, yeast and sugar. Let it foam up about 5 minutes. Add milk, eggs, butter, shortening, salt and flour. Mix with hands or you can do this in a mixer. Combine ingredients until a dough ball begins to form. Knead for about 10 minutes until smooth. Grease a large bowl and put dough inside and cover with plastic wrap. Put in oven with light on for about 45 minutes to an hour until it doubles in size.
After It is doubled in size flour your surface and punch down roll to out dough into 1/2 inch thick. Cut out circles with a round cookie cutter and use a piping tip to cut the middle hole out. You should have about 2 dozen or more doughnuts. Grease 2 baking sheets with oil and place doughnuts on them. Let them rise for another 45 minutes to an hour in the oven light on.
After they have doubled in size start heating your oil to 350 degrees. Squirt your dulce the leche in a bowl so you can dunk your doughnuts in there. Depending on how big your pot is, place 3-4 doughnuts in the oil and let them fry for about 50 seconds on each side until they are golden brown. Place on wire rack to drain the oil and dunk in dulce de leche while they are still warm. Repeat the process until all the doughnuts are done and enjoy.