Let’s break down the process into easy-to-follow steps.

Make the Cake:

Step 1: Preheat and Prepare Pan. Preheat your oven to 350°F (175°C). Butter a 9-inch springform pan and line the sides and bottom with parchment paper.

Step 2: Combine Dry Ingredients. In a medium bowl, whisk together 3 cups of the flour, baking powder, salt, spices (ginger, cinnamon, allspice, nutmeg), and granulated sugar.

Step 3: Incorporate Butter. Add the cubed cold butter to the dry ingredients and incorporate it with your hands until you have no large pieces left and the mixture resembles coarse sand.

Step 4: Combine Wet Ingredients. In another medium bowl, whisk together the eggs, heavy cream, and vanilla extract.

Step 5: Combine Wet and Dry. Add the wet ingredients to the dry ingredients and mix with a rubber spatula until just combined. Do not overmix.

Step 6: Prepare Apples. Toss the thinly sliced apples with the remaining 3 tablespoons of flour until evenly coated.

Step 7: Fold in Apples. Fold the floured apples into the cake batter.

Step 8: Transfer to Pan and Top. Transfer the cake batter to the prepared springform pan. Sprinkle the top evenly with demerara sugar.

Step 9: Bake. Bake until the apples are very tender and a toothpick inserted into the center of the cake comes out clean, about 1 hour and 20 minutes.

Step 10: Cool. Let the cake cool completely in the pan before removing the sides.

Make the Custard Sauce:

Step 1: Whisk Sugar and Yolks. In a heatproof bowl, whisk together the granulated sugar and egg yolks until lightened in color, about 6 minutes.

Step 2: Heat Cream and Vanilla. In a medium, heavy-bottomed saucepan over medium-low heat, add the vanilla bean seeds and pod (or vanilla extract if using) and the heavy cream. Cook the mixture, watching carefully, until it just comes to a boil.

Step 3: Temper Egg Yolks. Remove the cream mixture from the heat. Whisk a few tablespoons of the hot cream into the sugar-yolk mixture to temper the yolks. Gradually add in the remaining cream, whisking constantly.

Step 4: Cook Custard. Return the custard to the pot and continue to cook over medium-low heat, stirring constantly, until just thickened (do not boil!). Check the consistency by dipping a wooden spoon in, then running a finger along the back; the streak should stay intact.

Step 5: Strain and Cool. Immediately remove the custard from the heat and pour it through a fine-mesh strainer into a bowl. Let it cool completely.

Step 6: Serve. Once the cake and custard are cool, serve slices of the apple cake with a generous drizzle of the custard sauce.

These instructions are easy to do.