For strawberry sauce: In a medium saucepan, bring strawberries, sugar, orange zest and juice, and lemon juice to a boil over medium-high heat. Reduce heat, and simmer for 5 minutes. Transfer to the container of a blender, and add orange liqueur; purée until smooth. Let cool completely.
For custard: In the top of a double boiler, whisk together egg yolks and sugar. Add orange liqueur; cook over simmering water, whisking constantly, until mixture registers 165° on a candy thermometer, about 10 minutes. Place bowl in an ice water bath; whisk until custard is slightly cooled, about 1 minute. Set aside.
In the bowl of a stand mixer fitted with the whisk attachment, beat mascarpone at low speed until creamy, about 10 seconds. Increase mixer speed to medium-low. Gradually add cooled custard, beating until incorporated.
For whipped cream: In a medium chilled bowl, beat cream and 2 tablespoons sugar with a mixer at low speed until combined. Increase mixer speed to medium-high. Gradually add remaining 2 tablespoons sugar, beating until stiff peaks form. Fold whipped cream into custard.
Dip both sides of each ladyfinger in strawberry sauce. Set ladyfingers in two rows in an 11x7-inch baking pan. If needed, trim ladyfingers slightly to fit in pan. Spoon ¼ cup strawberry sauce over ladyfingers. Spread half of mascarpone mixture over ladyfingers. Repeat layers once. Chill overnight or at least 8 hours before serving. Top with strawberries and brush with orange marmalade, if desired.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/strawberry-tiramisu/