For the orange curd: Whisk together the granulated sugar, eggs, orange zest and juice, lemon juice and salt in a medium saucepan. Place over medium-low heat and cook, whisking constantly, until the mixture thickens to the consistency of a pudding, 7 to 8 minutes. Remove from the heat and stir in the butter a couple of cubes at a time. Set aside to cool.
For the trifle: Beat the heavy cream to stiff peaks in a large bowl with an electric mixer. In another bowl, stir together the mascarpone, confectioners' sugar and liqueur. Gently fold the mascarpone mixture into the whipped cream.
Dollop a quarter of the cream mixture on the bottom of a 3-quart trifle dish. Cover with a layer of ladyfingers, breaking them up if necessary to cover the bottom of the dish entirely. Spread a third of the curd over the cookies. Cover with about 1/2 cup of the raspberries, spreading them evenly. Dollop and spread one-quarter of the cream mixture on top of the raspberries. Repeat the layers of cookies, curd, raspberries and cream mixture 2 more times, ending with the cream mixture (the layers will depend on the size and shape of your dish; you might have more or less layers). Chill the trifle for at least 1 hour and up to overnight.
When ready to serve, decorate the top of the trifle with the orange slices and remaining raspberries.
You can chop the orange zest into even finer pieces to keep it from clumping together.