Whip the cream:
In a medium bowl, beat the thickened cream with an electric mixer to soft peaks.

Prepare the mascarpone mixture:
In a separate bowl, beat the mascarpone, sugar, vanilla extract, and 1 tablespoon orange juice for 30 seconds. Avoid over-mixing to prevent the mixture from splitting.

Mix in the zest:
Gently fold in the orange zest with a spatula.

Incorporate the whipped cream:
Carefully fold ⅓ of the whipped cream into the mascarpone mixture. Repeat two more times until fully incorporated.

Prepare the soaking liquid:
Combine the fresh orange juice and liqueur (if using) in a shallow dish large enough to fit the sponge fingers flat.

Soak the biscuits:
Quickly dip each Savoiardi biscuit into the soaking liquid and lay them side by side in a 9-inch square baking pan. Press them lightly to level them, trimming any that need to fit.

Assemble the layers:
Top the soaked biscuits with half of the mascarpone cream mixture, spreading it evenly with a spatula. Spread the orange curd over the cream layer.

Add another layer:
Add another layer of soaked Savoiardi biscuits, drizzle with any remaining orange juice mixture, and spread the remaining mascarpone mixture over the top.

Chill:
Refrigerate the tiramisu for 6 hours or overnight. For neat slices, freeze for 45-60 minutes before slicing, but ensure the dessert is not frozen solid.

Serve:
Garnish with orange slice quarters or zest right before serving.