Line a 4 1/2-by-8 1/2-inch loaf pan with 2 sheets of plastic wrap, leaving a 3-inch overhang on long sides. In a blender, puree raspberries and sugar, scraping down sides as needed. Strain through a fine-mesh sieve, pressing on solids; discard solids.
In a large bowl, whip cream until soft peaks form. With a rubber spatula, fold in lemon curd. Spoon 2 cups cream mixture into pan and smooth top. Dip ladyfingers in raspberry puree and arrange in pan, parallel to long edges. Pour remaining raspberry puree on ladyfingers. Top with remaining cream mixture and smooth top.
Wrap pan with overhanging plastic and freeze 8 hours (or up to 2 weeks). To serve, invert onto a serving platter, remove plastic, and slice.
The phrase semifreddo is Italian for "half cold" and refers to a partially frozen dessert.
My sister made this. A delicious, beautiful, simple. She served it with a swirl or more raspberry purée and a few fresh raspberries and blueberries. Happiness.