Step 1Heat the oven to 400 degrees. Put the cherries in a small (4-cup), well-buttered gratin dish. Sprinkle them with 1 tablespoon of sugar and the orange zest and stir to combine. Roast the cherries until they soften slightly and become fragrant, about 10 minutes.
Step 2In the meantime, grind together the almond meal and butter, one-third cup sugar, 3 egg yolks, orange liqueur and salt in a food processor.
Step 3Beat the egg whites until they hold soft peaks, add 1 teaspoon sugar and beat until they hold stiff peaks.
Step 4Add one-third of the egg whites to the food processor bowl and pulse to incorporate into the almond meal. Spoon the mixture into one side of the bowl with the egg whites, spread the egg whites over the top and fold the egg whites into the mixture until the topping is light and somewhat flowing. There may be small patches of unincorporated egg white; this is better than overfolding the batter and deflating it.
Step 5Spoon the egg white mixture over the top of the roasted cherries and sprinkle with 1 teaspoon sugar. Place the gratin dish on a cookie sheet to catch any spills and return to the oven to bake until the top is puffed and well-browned and a toothpick inserted in the center comes out clean, 20 to 25 minutes.