Warming a crisp won’t harm the flavor. It might harm the texture if it steams. I’d use either no lid or a loose foil to prevent over-browning.
This is a very good apple cake:
http://www.epicurious.com/recipes/food/views/marie-helenes-apple-cake-361150
I have made this one for years. It is similar to Marie-Helene’s but much tarter and a bit denser. This version came from Cuisinart magazine, so it was adapted for food processor. It is my favorite.
SENAUD’S APPLE CAKE
11/2 scant cups all-purpose flour (Use the lightly spoon into the cup and sweep method for measuring.)
1/4 teaspoon baking powder
13/4 sticks unsalted butter, softened
1 scant cup sugar
3 large eggs, separated
2 tablespoons dark rum
i medium lemon and 1 medium orange, or 2 lemons
11/2 pounds green apples, such as Granny Smiths, peeled, quartered or halved, and cored.
Preheat the oven to 350 degrees. Butter and flour a 9-inch round cake pan.
Use a vegetable peeler to remove the zest of the citrus fruit in strips, reserve.
Slice apples (1/4 in)in food processor or by hand, should have about 3 cups. Toss with some lemon juice in a bowl and reserve.
Process the citrus zest and 1/2 cup sugar until finely chopped. Add remaining sugar and butter, process about 20 sec until creamy. Add egg yolks and rum, process about 20 sec, scraping bowl once.
In a separate bowl, whisk together the flour and baking powder. Add to processor, pulse until flour just disappears.
In a separate bowl, beat egg whites until stiff. Stir 1/4 of them into the flour mixture to lighten, then fold in the remainder. (You can stir the first part in the processor bowl, then scrape it all out into the egg white bowl for folding.)
Cover bottom of prepared pan with 1/3 of batter, layer with 1/2 the apples, repeat. End with the last third of batter on top. The batter will be very thick. Perfect coverage is not necessary. Better not to deflate the batter too much.
Bake 1 1/4-1/2 hrs until tester comes out clean. Let cool on a rack 1/2 hr before unmolding. This cake travels really well and is great for picnics.