Combine all ingredients except lemon zest in a medium sauce pot and simmer for 15-20 mins.
Puree in a blender on high and strain through a fine sieve strainer or chinoise. Cool and store in a squeeze bottle. To plate, stick squeeze bottle nozzle into the donuts and fill gently.
Blueberry Glaze
Combine all ingredients in a mixing bowl with a whisk adding extra powdered sugar if needed to thicken. Set aside for dipping later.
Fill donuts with blackberry filling then dip in the blueberry glaze. Serve as is or with fruit and powder sugar if desired.
Donuts:
Combine all ingredients for dough except hot water and mix well. Slowly add hot water and keep mixing with a spatula. It should look really wet. Cover and set aside for 1 to 2 hours.
Mix dough again with a spatula.
Brush a thin layer of oil on a cookie sheet. Heat frying oil to 350°F over high heat.
Meanwhile, divide dough into 14-16 little doughnuts. Roll them with the palms of your hands and place on oiled cookie sheet.
Place doughnuts one by one into hot oil, about 4-6 at a time. They will increase in size, so do not crowd pot.
As soon as the dough is puffed up, turn off heat and keep frying until fully cooked and golden, about 3-4 minutes. Continue to rotate evenly in oil to ensure even cooking.
Remove from pan, drain excess oil and rest on cold towels
