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1
Preheat the oven to 350 degrees F. Grease a 13 by 9 by 2-inch rectangle pan with 1 teaspoon of the butter.
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2
In a medium-size nonreactive saucepan, melt 2 tablespoons of the butter.
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3
Add the brown sugar, persimmons, and the lemon juice.
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4
Saute the mixture for 2 to 3 minutes, or until softened.
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5
In a small bowl, dissolve the cornstarch in the water.
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6
Add to the persimmon mixture and cook, stirring, until it thickens, about 2 minutes.
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7
Remove from the heat and let cool completely.
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8
In a large mixing bowl, cream 1/4 pound (1 stick) of the butter and the light brown sugar with an electric mixer.
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9
Add the eggs 1 at a time, beating well after each addition.
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10
Into a medium-size mixing bowl, sift 3 1/2 cups of the flour, the baking powder, baking soda, 1 teaspoon of the cinnamon, and the salt.
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11
Add the flour mixture, buttermilk, and vanilla to the butter mixture and beat with the electric mixer until everything is incorporated.
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12
In another medium-size mixing bowl, combine the remaining 1/4 cup (1/2 stick) butter, the remaining 1/2 cup flour, the remaining 1/2 cup brown sugar, and the remaining 1/4 teaspoon cinnamon.
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13
Using your hands, combine the mixture until it resembles fine crumbs.
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14
Spread half of the batter in the prepared pan.
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15
Spread the persimmon mixture over the batter.
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16
Drop heaping spoonfuls of the remaining batter over the persimmon mixture, about 1-inch apart.
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17
Sprinkle the crumb mixture evenly over the surface.
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18
Put the cake pan on a baking sheet and bake until golden brown, about 30 to 35 minutes.
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19
Remove from the oven and let cool slightly.
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20
In a medium-size mixing bowl, whisk together the confectioners' sugar, dark Karo, and milk until smooth.
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21
Drizzle the frosting over the top of the coffee cake.
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22
Cut into slices and serve warm.
