Instructions

for the crêpes

Combine egg, milk, water, flour, cognac, sugar, salt, and melted butter in blender until smooth batter forms, about 10 seconds. Transfer batter to medium bowl.
Using pastry brush, brush bottom and sides of 10-inch nonstick skillet very lightly with melted butter; heat skillet over medium heat. When butter stops sizzling, tilt pan slightly to right and begin pouring in scant 1/4 cup batter. Continue to pour batter in slow, steady stream, rotating wrist and twirling pan slowly counterclockwise until pan bottom is covered with even layer of batter. Cook until crêpe starts to lose opaqueness and turns spotty light golden brown on bottom, loosening crêpe from side of pan with rubber spatula, 30 seconds to 1 minute. To flip crêpe, loosen edge with rubber spatula and, with fingertips on top side, slide spatula under crêpe and flip. Cook until dry on second side, about 20 seconds.
Place cooked crêpe on plate and repeat cooking process with remaining batter, brushing pan very lightly with butter before making each crêpe. As they are done, stack crêpes on plate (you will need 4 crêpes). (Crêpes can be double-wrapped in plastic and refrigerated up to 3 days. If crêpes have been refrigerated, bring them to room temperature before making sauce.)

for the orange sauce

Adjust oven rack to lower-middle position and heat broiler. Add 1 tablespoon cognac to broilersafe 10-inch skillet; set over medium heat just until vapors begin to rise from cognac, about 5 seconds. Remove pan from heat and wave lit chimney match over cognac until it ignites; shake pan until flames subside. (Cognac should burn for about 15 seconds; re-ignite if flame dies too soon.)
Add butter, 1 tablespoon sugar, and 1/4 cup orange juice to cognac; simmer briskly over high heat, whisking occasionally, until many large bubbles appear and mixture reduces to thick syrup, 3 to 5 minutes. (You should have just under 1/4 cup sauce.) Transfer sauce to small bowl; do not wash skillet. Stir remaining orange juice, zest, liqueur, and remaining cognac into sauce. Cover to keep warm.

to assemble

Fold each crêpe in half, then in half again to form wedge shape. Arrange folded crêpes in now-empty skillet, with wedge points facing inward, so the four points meet in the middle. Sprinkle crêpes evenly with remaining sugar. Place skillet in oven and broil until sugar caramelizes and crêpes turn spotty brown, about 3-5 minutes. (Watch crêpes constantly to prevent scorching; turn pan as necessary.) Remove pan from oven and pour half of sauce over crêpes, leaving some areas unsauced. Transfer crêpes to individual serving dishes and serve immediately, passing extra sauce separately.