Preheat oven to 350 degrees . Slice 1/3 inch off ends of kiwis and press pulp from ends into fine-mesh sieve set over bowl of milk to extract juice; set aside for 10 minutes to curdle.
Meanwhile, peel kiwis and slice crosswise very thinly. In bowl, combine flour, baking powder, baking soda, cinnamon and salt. Using mixer, beat butter and sugar on medium speed until light and fluffy, 5 minutes. Beat in eggs, 1 at a time, beating after each addition. With mixer on low speed, alternately incorporate dry and milk mixtures in 3 parts.
Pour batter into buttered 10-inch cast-iron skillet and arrange kiwi slices on top. Bake until toothpick inserted in center comes out clean, about 40 minutes.