Whisk flour, and lemon zest in a medium bowl. In another bowl, whisk together the milk, egg and 1 tablespoon sugar. Slowly whisk the egg mixture into the flour mixture until smooth. Let it stand for few minutes until the bubbles are gone.
In a 12 inch pan or crepe pan, lightly brush the pan with melted butter and heat over medium high heat. Pour 5 to 6 tablespoons (about ¼ cup) of batter and tilt the pan to coat. Cook for 1 to 2 minutes and flip with a thin spatula to cook the other side about 1 more minute. Cook the remaining batter. Stack the pancakes on a plate.
Berry Filling:
Heat the jam in a small pan over low heat. Add the berries and lemon juice. Cook until warm and syrupy. Set aside.
Custard Sauce:
In an small saucepan, combine sugar, cornstarch and salt until well blended. Add the milk and cook over low heat until almost boiling. Remove from the heat. In a small bowl, whisk together the egg yolk and vanilla until blended. Add a couple of tablespoons from milk mixture to egg yolk mixture. Whisk in the yolk mixture and cook over low heat until sauce begins to thicken.
Assemble the crepes:
Spread berry filling in a line down center of each crepe and roll. Top with more fresh berries if you have. Drizzle the custard sauce and sprinkle with confectioner's sugar. Serve
Recipe by The Gluten Free at https://www.theglutenfree.com/gluten-free-berry-lemon-crepes-with-custard-sauce/