Lemon Curd: In a medium saucepan, whisk eggs and sugar until light and glossy. Add lemon juice, zest, and salt; cook over medium-low heat, whisking constantly, until it thickens slightly (about 3-4 minutes). Whisk in butter one tablespoon at a time until melted, then continue whisking for another 5-6 minutes until it thickens enough to coat the back of a spoon. Stir in vanilla, strain through a fine mesh strainer, and chill for 2 hours.
Lemon Syrup: Combine all ingredients in a small saucepan and boil until sugar dissolves; cool completely.
Mascarpone Cream: Whip cream to soft peaks, add sugar slowly and whip to stiff peaks. Mix in ½ cup lemon curd and mascarpone until smooth, then fold in whipped cream, vanilla, and zest.
Assembly: Dip half the ladyfingers in lemon syrup, layer on dish, top with half the cream mixture, then ½ cup lemon curd. Repeat with remaining ingredients. Chill for at least 2 hours. Garnish with lemon slices and mint leaves.