Step 1

Preheat the oven to 375°F (190°C). Lightly oil an 8- or 9-inch springform pan. Dust the pan with flour and tap out any excess.

Step 2

In a large bowl, whisk together the flour, almond meal, baking powder, and salt. In a separate bowl, whisk together the oil, egg, half-and-half (or milk, if using), lemon juice and zest, the 1 cup (8 ounces) sugar, and the almond extract until thoroughly combined. Add the liquid ingredients to the flour mixture and whisk just until combined.

Step 3

Scrape the batter into the prepared pan. Arrange the plum halves, cut side up, atop the batter. In a bowl, combine the almonds, the remaining 2 tablespoons sugar, and the butter and mix well. Dot the almond topping over the cake.

Step 4

Bake the cake until the surface is golden brown and a tester inserted in the center of the cake comes out clean, about 45 minutes. (If using an 8-inch pan, you may need to bake it longer, being careful to cover the outer edges of the cake with a strip of foil if they begin to brown.) Transfer the pan to a wire rack and let cool for 20 minutes. Remove the ring from the pan and place the cake on a serving platter. Cut into wedges and serve warm or, if you can wait, at room temperature.