Inspired by Kate Middleton’s royal wedding cake, these petits fours consist of a traditional British fruitcake, also chosen by Princess Diana for her wedding. To decorate the petits fours with flowers — as Princess Kate’s cake will be — look for icing rose and narcissus blossoms; available at beryls.com.
For the cake: Combine first 5 ingredients in a large bowl.
Cover and let macerate overnight at room temperature, stirring occasionally.
Preheat oven to 325 degrees F.
Butter a large rimmed baking sheet (about 18 x 13 x 1"); line with parchment paper.
Whisk flour, salt, cardamom and nutmeg in a large bowl.
Beat both sugars and almond paste on low speed in a large bowl until mixture resembles a coarse meal.
Add butter; beat on medium speed until light and fluffy, about 7 minutes.
Add eggs and vanilla; beat to blend.
Add flour mixture in three batches, beating just to blend each batch.
Add walnuts and dried fruit mixture with soaking liquid; stir batter just to blend.
Spread batter evenly in prepared pan and bake until a toothpick inserted into center of cake comes out clean, about 45 minutes.
Transfer to a wire rack and let cool completely.
Set a wire rack in a large rimmed baking sheet lined with parchment paper.
Invert cake onto a work surface; peel off parchment paper.
Trim 1/2 inch from all four sides.
Cut cake into 1 1/2-inch squares.
Place squares on wire rack.
For the white chocolate ganache glaze: Place chopped white chocolate in a medium heatproof bowl.
Stir cream and corn syrup in a medium saucepan over low heat until mixture begins to simmer.
Pour over white chocolate and let sit for 3 minutes, then stir until melted and smooth.
Let cool slightly, stirring occasionally, until glaze is slightly thickened but still pourable.
Spoon glaze evenly over cakes to coat tops and sides.
Refrigerate cakes on rack until glaze is set, about 30 minutes.
Spoon a second layer of glaze over cakes.
Refrigerate for another for 30 minutes.
Decorate petits fours.
Transfer to platter.