Step 1: Roast sweet potato in a high-heat oven, or in a microwave, until soft. Allow to cool, then peel. With a fork, mash into a smooth puree.
Step 2: Melt butter, and set aside. In the the same pan, slightly heat up the milk (no hotter than 105 degrees), transfer to a bowl, and mix in the yeast. Set aside.
Step 3: Mix together all of the ingredients: sweet potato puree, melted (cooled) butter, milk with yeast, flour, salt, sugar, ricotta, egg, egg yolks, and vanilla extract. this can be done in a bowl by hand, with an electric mixer and dough hook, or in a bread maker.
Step 4: Once dough comes together, place in a oiled bowl and cover in plastic wrap, or with a kitchen towel. Allow to rise at room temperature for 1 hour.
Step 5: Once the dough doubles in size (about 1 hour), roll it out on a floured countertop (about ½ inch thick). Using a 1.5 inch cookie cutter, cut out circles, and place on parchment-lined baking sheets. Cover baking sheets with kitchen towels, and allow to rest for another hour.
Step 6: Preheat oven to 400 degrees. Bake doughnut holes for about 8-10 minutes, or until tops are golden (make sure not to overcook). Allow to cool before dipping in glaze.
Step 7: While doughnuts are rising for the second time, prep the glaze: whisk caster sugar, milk, maple syrup, vanilla extract, and cinnamon together. Set aside.
Step 8: Dip cooled doughnuts in the glaze. Allow the glaze to set, about 10 minutes. Serve!
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