Used in the curd and the candied topping, Meyer lemons subtly elevate this luscious dessert. The candied lemons, crepes, and filling are all make-ahead ingredients that can assembled just before serving.
Whisk together flour, sugar, and salt. Whisk together milk, eggs, and vanilla. Gradually pour milk mixture into flour mixture, whisking until smooth. Whisk in butter. Pour through a fine sieve into an airtight container; discard lumps. Refrigerate at least 2 hours or overnight.
Lightly coat a 6-inch crepe pan or nonstick skillet with butter. Heat over medium heat until just starting to smoke. Remove from heat; pour about 2 tablespoons batter into center. Swirl to cover bottom. Reduce heat to medium-low; return pan to heat. Cook until edges are golden and center is dry, about 30 seconds per side.
Slide crepe onto an overturned plate. Repeat with remaining batter, coating pan with butter as needed, and stacking crepes. Let cool.
Place 1 crepe on a flat serving dish. Spread about 1/4 cup lemon curd mousse onto crepe. Top with 1 crepe. Continue layering crepes and mousse. (Use 15 crepes, ending with a crepe on top.) Refrigerate until firm, about 1 hour.
Top crepe cake with whipped cream and 3 or 4 candied lemon slices.
Plain crepes can be refrigerated for up to 1 day.