10tablespoons140 g unsalted butter, at room temperature
1cup200 g granulated sugar
2eggsat room temperature
½cup102 ml whole milk, at room temperature
1cup120 g all-purpose flour
½cup60 g almond flour
¼cup35 g whole-wheat flour
4plumscut into 6 or 8 pieces
2tablespoonsunsalted buttercold, cut into ¼-inch cubes
Preheat the oven to 375°F. Generously grease a 9-inch springform pan, then line the bottom and sides with greased parchment paper.
In a food processor, combine the butter, sugar, eggs, milk, and vanilla and process until smooth. Add all three flours, the baking powder, and salt and mix together by pulsing several times, just until smooth.
Scrape the batter into the prepared pan and smooth the top with a spatula. Gently tap the pan on the counter several times to release excess air bubbles. Add the plums in a spiral on top of the batter. Set the pan on a baking sheet.
Bake for about 45 minutes.
To make the topping: in a small bowl, mix together the sugar and cinnamon.
Carefully sprinkle the topping over the baked cake and then dot with the butter.
Continue baking until the cake is golden and a tester comes out clean, about 20 minutes. Let the cake cool in the pan for 20 minutes and then run a knife around the edge. Remove the sides of the springform and transfer to a wire rack to cool completely before serving.
I made the following high altitude changes: reduced baking powder to ½ teaspoon, removed 1 tablespoon sugar from the 1 cup, 1 cup + 2 tablespoons flour. I baked it at 400° for 40 minutes and then baked it another 15 minutes after adding the topping.