Prepare the pan. Preheat an oven to 350°F (177°C). Line a 9-inch cake pan or springform pan with parchment paper, then grease the sides with nonstick baking spray.
Cream the butter and sugar. Combine 8 Tbsp (113g) butter and 5 Tbsp sugar in the bowl of a stand mixer fitted with paddle attachment. Beat on medium speed until the mixture is pale and fluffy, about 2-3 minutes. Use a spatula to scrape down the sides.
Add almond flour. Add 1½ cups (165g) almond flour and ¼ tsp kosher salt, then mix until well blended.
Add eggs. Beat in the eggs one at a time, mixing well after each addition. Scrape down the sides, then add 2 tsp Amaretto and 1 tsp vanilla extract and beat once more.
Prepare the apples. Peel, core, and halve or quarter the apples. (You can cut out the core after halving/quartering if you don’t have an apple corer.) Slice each half thinly (about ¼-inch thick), keeping the slices together so the shape of each segment is mostly intact.
Assemble the cake. Spoon the batter into the prepared pan and smooth the top with an offset spatula. Arrange the apple segments decoratively on top, cut side down, pressing them gently into the batter so they sink slightly. Sprinkle the top evenly with 1 Tbsp turbinado sugar and a light dusting of cardamom (about ¼ tsp).
Bake the cake. Transfer to a preheated oven, then bake until the cake has puffed up, is golden brown, and the edges pull slightly away from the sides of the pan, about 40-45 minutes. The apples will soften and sink into the batter as it bakes, creating a beautiful rustic pattern on top.
Cool and serve. Allow the cake to cool in the pan for 10-15 minutes, then release the springform pan and transfer to a wire rack (or run a knife along the edges to help loosen it, then invert onto a wire rack). Enjoy warm or at room temperature with a dusting of powdered sugar and a generous dollop of crème fraîche, whipped cream, or ice cream.