3 pounds mixed apples peeled, cored,
and cut into 1/8" thick slices
1 vanilla bean halved lengthwise
1 lemon zested
1 tablespoon freshly-squeezed lemon juice
cup sugar or more to taste
8 slcs firm white bread - (to 10) crusts removed
2 cups milk
(or 1 tspn vanilla extract)
Remove the cover, increase the heat if necessary for the apples to be bubbling vigorously, and continue cooking, stirring frequently, until any liquid has evaporated and the thickened apple mixture moves around as a mass when you stir it, about 15 minutes. It may caramelize in spots, but watch it so it doesn't get too dark.
Prepare the Crust: Cut about 4 slices of the bread in half to form triangles, and then cut those triangles in half. Brush 1 side of each triangle lightly with butter, and arrange them in the base of the prepared mold, buttered-side down, so they completely cover the bottom. If there are any spaces, fill them in with pieces of bread that are cut to fit.
Cut the remaining bread slices into 14 to 16 (1-inch) wide strips, and trim them so they are just long enough to reach the top of the mold. Lightly brush each with clarified butter, and arrange them, buttered-side out, upright along the sides of the mold to completely line it, overlapping them slightly. Set aside the extra bread strips.
Transfer the charlotte mold to a wire rack and let it cool for 15 minutes. Then, place a serving plate over the top of the mold and carefully flip it over. The charlotte will slide right out. Because of its pudding-like consistency, use 2 large spoons to cut the charlotte. Serve it warm or at room temperature, with the Vanilla Custard Sauce alongside.
Meanwhile, whisk the egg yolks and the sugar together in a medium bowl until pale yellow and thick.
Strain the hot milk into a bowl, and discard the vanilla bean. Whisk the milk into the egg yolk mixture, add the vanilla extract, if using, and return it to the saucepan. Cook, stirring constantly, over medium-low heat until the custard has thickened enough to coat the back of a spoon, 8 to 10 minutes. Be careful not to let the custard curdle.