Instructions for donuts:
In a stand mixer with dough hook attachment, add dry ingredients to bowl of mixer. In a separate small bowl, add 3 tbsp of lukewarm water and sprinkle yeast and one teaspoon of sugar on top. Set aside for 5 minutes, until yeast mixture is foamy.
Make a well in the center of the dry ingredients, then pour in the buttermilk, egg, melted butter and yeast mixture. Mix with the dough hook until a dough forms, about 5 minutes.
Cover with a dish towel and set aside until at least doubled in size, about an hour.
Once the dough has doubled, place it on a floured surface and knead lightly. Using a rolling pin, roll out to 1/2″ thickness. Cut with a round, sharp cookie cutter (about 3″ diameter). Re-knead to scraps and repeat until 8 donuts are cut.
Place each doughnut on a piece of parchment or waxed paper, then place on a cookie sheet. Place in a warm, draft free place (like an oven with the oven light on), for another hour, until risen again.
In a heavy bottomed pan or Dutch oven, heat oil to about 350ºF
Carefully place the doughnuts into the hot oil. Turn once as soon as they become golden brown on the underside and remove them and place on a paper towel lined plate to cool slightly.
Instructions for Hibiscus Cream:
In a medium saucepan, heat the milk and hibiscus leaves to a boil over medium heat. Immediately turn off the heat and set aside to infuse for 15 minutes.
In a bowl, whisk the egg yolks and sugar until light and fluffy.
Add the cornstarch and whisk vigorously until no lumps remain. Whisk in 1/4 cup of the hot milk mixture until incorporated.
Whisk in the remaining hot milk mixture, reserving the saucepan. Pour the mixture through a strainer back into the saucepan. Cook over medium-high heat, whisking constantly, until thickened and slowly boiling. Remove from the heat and stir in the butter.
Let cool slightly. Cover with plastic wrap, lightly pressing the plastic against the surface to prevent a skin from forming.
Chill at least 2 hours or until ready to pipe (the custard can be made up to 24 hours in advance)
Place cooled pastry cream in a pastry bag with tip attachment.
Roll donuts in cinnamon sugar mixture. Insert piping bag tip into end of donut and fill.