Once upon a time I had the most delicious passion fruit curd filled donut this planet has ever seen (or tasted.) I swore that very day I would do my best to make my own curd filled homemade donuts, and it starts now with these blackberry beauties.
Combine warm water, yeast, and a pinch of sugar in a mug to activate the yeast. Allow to proof for 5 minutes in a warm place.
Pour 1 cup of the bread flour into a large bowl, and stir in the water and yeast mixture with a whisk to make the starter dough. Allow to sit for 30 minutes, uncovered, in warm place.
Combine the eggs, sugar, salt and melted butter and mix well. Add the remaining bread flour and stir with a large spatula until it is fully incorporated.
Place the dough on a well floured countertop and knead until soft and smooth—the dough will be sticky, but avoid adding too much additional flour.
Place in a clean, greased bowl, cover with plastic wrap, and allow to rest in a warm place until double in size (about 1 hour). Meanwhile, prepare the blackberry curd filling (see below).
Once doubled in size, place on a lightly oiled and floured countertop and flatten the dough with the palms of your hand until the it is about ¾" thick. Using a 3-inch biscuit cutter, shape the donuts and place each piece on a baking sheet or parchment paper. Cover the doughnuts with a kitchen towel and allow to rest for 15 minutes before frying.
Making the Blackberry Curd:
Puree your blackberries in a blender. Using cheesecloth or a fine mesh sieve, strain the seeds from the blackberries into a medium sized bowl.
In a medium saucepan, combine the sugar and cornstarch and whisk together. Add in the blackberry puree, lemon juice and eggs. Heat on medium until it comes to a boil, stirring constantly. Remove from heat and stir another minute until it is thick, and then add the butter.
Place your curd in a bowl and refrigerate for at least one hour. Make sure you cover it with plastic wrap so it doesn't form a skin.
Frying and Preparing the Donuts:
In a large pot or deep fryer, heat the shortening to 375˚F. Fry 3-4 donuts at a time for about 4-5 minutes on each side, or until golden brown. Use a candy thermometer to make sure the liquid isn't too hot, or else the dough will burn on the outside and won't be fully cooked on the inside.
Place finished donuts on a paper towel to drain and cool. Once they are warm to the touch, generously cover them in granulated sugar on both sides. Then, use a paring knife to make a tiny hole and use a piping tip to insert about 1 tablespoon of blackberry curd per donut.