Line the bottom and all four sides of a 6-cup loaf pan with parchment paper. Position a rack in the lower third of the oven and preheat the oven to 350° F degrees.
Whisk to combine the rice and buckwheat flours, baking soda, nutmeg, and salt. Set aside.
Combine the butter, sugar, and eggs in the bowl of a stand mixer and beat on medium speed with the paddle attachment until thickened and lighter in color, about 2 minutes. Or beat with the handheld mixer in a large bowl on medium-high speed for 3 to 4 minutes.
Add the flour mixture, persimmon, currants, and walnuts and beat on low speed until smooth. Scrape into the lined pan and spread evenly.
Bake the loaf for 45 to 50 minutes (please check this, it might be a bit longer), until a toothpick inserted in the center comes out clean. Cool the loaf on a rack, at least 2 hours, before unmolding and slicing (with a serrated knife)—flavors marry and the cake becomes moister over several hours or a day. Wrapped airtight, the cake keeps for 2 or 3 days; it keeps for longer in the refrigerator.
My career was sparked by a single bite of a chocolate truffle, made by my Paris landlady in 1972. I returned home to open this country’s first chocolate bakery and dessert shop, Cocolat, and I am often “blamed” for introducing chocolate truffles to America. Today I am the James Beard Foundation and IACP award-winning author of ten cookbooks, teach a chocolate dessert class on Craftsy.com, and work with some of the world’s best chocolate companies. In 2018, I won the IACP Award for Best Food-Focused Column (this one!).