Preheat oven to 350°F. Grease and line two 8-inch round cake pans with parchment.
Melt the white chocolate for the batter and set aside to cool until slightly thickened.
Whisk flour, baking powder, baking soda, and the cake salt in a medium bowl.
Cream softened butter and granulated sugar until very fluffy, about 3 minutes.
Beat in eggs one at a time, then mix in vanilla. Scrape the bowl well.
Stir in the cooled melted white chocolate for the batter until fully combined.
Add dry ingredients in three additions, alternating with buttermilk. Mix just until smooth.
Divide batter between pans and level the tops. Tap pans gently to release air.
Bake 30 to 35 minutes, until a toothpick comes out clean. Cool 10 minutes in pans.
Turn cakes out to a rack and cool completely before filling and frosting.
For frosting, melt the remaining white chocolate and let it cool until slightly thick.
Beat softened butter and frosting salt until creamy. Gradually add powdered sugar.
Mix in cooled melted white chocolate and vanilla. Beat in cream until silky and spreadable.
Stir preserves with half the raspberries and the lemon zest, lightly smashing the berries.
Place one cake layer on a stand. Spread raspberry filling, leaving a 1/2-inch border.
Set on the second layer. Apply a thin crumb coat, chill 15 minutes, then frost generously.
Decorate with remaining raspberries. Slice with a warm knife for clean cuts.