Step 1Peel each quince, cut it into quarters and remove the tough core from each quarter. Place the cleaned quince in a bowl of water to which you've added the juice of half a lemon. Then proceed on to the next quince. (Those same phenolic compounds encourage enzymatic browning, which can be prevented by keeping the quince away from oxygen and treating it with acidity.)
Step 2When all of the quinces have been cleaned, combine one-third cup water and the sugar in a medium saucepan and place over medium heat. Cut a cheesecloth square and place the cloves, cinnamon and allspice in the center. Gather the corners and tie them together with string to form a pouch; add it to the water.
Step 3Chop each quince quarter into half-inch chunks and add them to the water. Cover the pan tightly and cook at a quick simmer, stirring occasionally, until the quince has softened and turned rosy, 1 1/2 to 2 hours.
Step 4When the quince is cooked, remove the lid and increase the heat to medium-high to reduce the syrup, if necessary. You should have something like a sticky, chunky, very aromatic applesauce. Remove the spice bag, stir in the juice of the remaining one-half lemon and set aside off the heat.
Step 5Place the walnuts in a small, dry skillet and toast over medium heat until they are aromatic and just beginning to brown, about 4 minutes. (Judge by color and aroma change, McGee says, not the texture because "heat softens the tissue, which [will then get] crisp as it cools.") Empty the nuts into a bowl to keep them from scorching and set aside. The recipe can be prepared to this point a day ahead; the quince should be emptied into a tightly covered container and refrigerated until ready to use.
Step 1Pulse three-fourths cup milk, the water and the eggs 2 or 3 times in a blender until smooth. Add 1 tablespoon sugar, the cinnamon, salt and flour. Blend the batter until smooth.
Step 2With the blender running, add the melted butter. The batter should be the thickness of heavy cream. If necessary, add up to one-fourth cup more milk to correct the thickness. Strain the batter into a covered bowl and refrigerate at least 1 hour. (You need to let the crepes rest after blending, McGee says, "to allow the proteins and damaged starch to absorb water and air bubbles to rise and escape." If you cook them too early, you'll wind up with "holey" crepes.)
Step 3Heat an 8- to 9-inch crepe pan (a nonstick skillet with a flat bottom) over medium-high heat until a few drops of water skitter and dance when sprinkled on the surface. Add one-half tablespoon cold butter and swirl the pan to distribute it across the surface. Wipe any excess butter from the skillet with a paper towel and return the pan to the heat.
Step 4Holding the skillet off the heat, pour in a scant one-fourth cup batter. Swirl the batter quickly across to fill the bottom of the skillet. Return the skillet to the heat and cook until the edges of the crepe begin to brown, about 30 seconds. Using a small spatula or a table knife, lift the edges of the crepe. Grab the edges with your fingertips and quickly flip it over. Cook the uncooked side just until the crepe slides free in the pan, about 30 seconds. Remove to a plate and cover it with wax paper.
Step 5Repeat until all of the batter is used, adding the remaining one-half tablespoon butter as needed. You should have 12 crepes. Crepes can be stored, tightly sealed, in the refrigerator.
Step 6When you're ready to finish the recipe, heat the oven to 350 degrees and butter a large oval gratin dish.
Step 7Place 1 crepe on a work surface and spread about 2 tablespoons of the quince mixture onto half of the circle. Sprinkle 1 tablespoon walnuts over the quince. Fold the crepe into a quarter and place it in the gratin dish.
Step 8Repeat to use all of the quince mixture, walnuts and crepes, arranging the crepes in a single overlapping layer. Place the gratin dish in the oven to crisp the top and heat through, about 20 minutes.
Step 9Beat the cream with a whisk until foamy. Add the remaining 1 tablespoon sugar and continue beating until you can form a medium-stiff peak when you lift the whisk from the cream. (Be sure the cream is very cold; McGee reminds that "even mild warmth softens the butterfat skeleton of a cream foam, and a liquid fat will collapse the air bubbles.") Beat in the Bourbon. Taste and, if necessary, add a little more sugar.
Step 10When the crepes have barely crisped on top and the quince mixture is heated through, serve immediately, passing the whipped cream on the side.