This type of persimmons is not simiular to the Hachiya persimmon in consistancy. This is the kind we grow in FL. I also found recipes on the net for them from CA. This type of persimmon needs to be blanched and peeled like a tomatoe. It is then grated, sliced or diced. It the firmness and likes of an apple.
In small bowl mix persimmons and baking soda, set aside.
In large bowl cream butter, sugar, evaporated milk and eggs together. Stir baking powder into flour or sift together. Slowly add flour mixture to creamed. Then add the persimmons and stir until well distributed in batter. Pour into a 9x13 greased pan.
Bake at 350 degrees for about 45 min or until toothpick comes clean.
For the topping--put a small pot on the stove and combine sugar, evaporated milk and butter. Let come to boil. When sugar is dissolved take off heat and add vanilla.
Take a butter knife and make lots of slits. This doesn't look pretty but it get the topping to seep in well. Pour topping into center of cake and spread all over, making sure it goes in between the cake and the pan. Let sit till cooled. The topping will firm up. Cut and serve.