In a large bowl, whisk eggs, milk, melted butter, sugar, and salt. Gradually add the flour, whisking until smooth.
Rest the batter for 30 minutes to ensure tender crêpes.
Heat a non-stick skillet or crêpe pan over medium heat and lightly grease with butter.
Pour 1/4 cup of batter into the pan, swirling to spread it thinly.
Cook for 1-2 minutes until golden on the underside, then flip and cook for 30 seconds.
Repeat until all batter is used, stacking crêpes with parchment paper between them.
Melt butter in a large skillet over medium heat. Add sugar and stir until dissolved and golden.
Stir in orange juice, zest, and lemon juice (if using). Simmer for 2-3 minutes to thicken slightly.
Fold each crêpe into quarters or roll them up, then add them to the skillet with the sauce.
Spoon sauce over the crêpes and let them warm for 1-2 minutes.
Remove the skillet from heat. Pour in Grand Marnier or Cointreau and carefully ignite with a long match or lighter.
Allow the flames to subside while swirling the pan gently.
Plate the crêpes, spoon extra sauce over the top, and serve immediately.
Garnish with whipped cream, vanilla ice cream, or toasted almonds for added flair (optional)