Preheat oven to 350°F (180°C). Butter a 9-inch springform pan. Line bottom of pan with parchment paper.
In the container of a blender, place Hachiya persimmon and buttermilk; process until smooth. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In a medium bowl, whisk together flour, cinnamon, baking powder, baking soda, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with buttermilk mixture, beginning and ending with flour mixture, beating just until combined after each addition. Fold in Fuyu persimmons. Spread batter in prepared pan.
Bake until a wooden pick inserted in center comes out clean, about 1 hour, covering with foil halfway through baking to prevent excess browning. Let cool in pan for 15 minutes. Remove from pan, and let cool completely on a wire rack. Spread Honey Buttercream on top of cake. Top with Sugared Persimmons.
Notes
*We used Président.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/cinnamon-persimmon-cake/