Very key here is the size of your loaf pan because this will fill out every speck of it before it is done. Mine holds 6 liquid cups (or 1420 ml); it’s 8×4 inches on the bottom and 9×5 inches on the top. If yours is even slightly smaller or you’re nervous, go ahead and pour a little of the apple and batter mixture into a few muffin cups and bake them off. They will not go to waste.
Prepare pan: (See Note at the end about loaf pan size.) Coat the short ends of a loaf pan with butter or nonstick spray. Line the bottom and two long sides of the pan with a piece of parchment paper. Place loaf pan on a rimmed baking sheet, just in case there’s overflow.
Prepare apples: Peel and core your apples, then slice them very thin (about 1/8-inch or 1/3-cm thick). A mandoline (this is mine) works great for this. Place apples in a large bowl and gently toss with lemon juice.
Make cake batter: Melt butter in a medium bowl. Whisk in sugar and salt, then eggs and vanilla until evenly incorporated. Whisk in flour until smooth, then milk. Pour batter over sliced apples, then stir and turn the apples a few times so that they’re evenly coated. This is much easier to do with your (clean) hands.
Assemble cake: Once again, using your hands is easiest for this. Push about a dozen full slices to the side of the bowl for the final layer. Arrange the remaining apple slices slightly overlapped around the prepared loaf pan, pushing the straight edges against the sides for the neatest appearance. Use any smaller or broken apples to fill any center gap. By the time I’m down to just batter and a few scraps of apple, I just pour it over and then use my hands to push the pieces around until it’s level. Tap the pan on the counter a few times to release any trapped air bubbles. Use the apple slices you pushed aside to decorate the top, fanning them into a flower pattern if you wish.
Bake the cake: For 60 to 70 minutes, or until a toothpick or skewer inserted into the center of the cake comes out batter free and doesn’t feel like it’s spearing any raw/crunchy apples. Transfer to a cooling rack for 5 minutes, then brush top with warmed apricot preserves and let cool completely in the pan. The cake will be puffed at first, and will settle flat as it cools.
Serve: Once cooled to room temperature, use a knife to loosen the cake from the short ends of the pan. Use the sling of parchment paper around the longer sides of the cake to help lift it out of the pan. Remove parchment paper and transfer to a serving plate. Cut into slices. Dust with powdered sugar, if using.
Do ahead: This cake keeps fantastically in the fridge for 5 to 6 days. Bring back to room temperature before serving.
