Place the raspberries, 1 tbsp of sugar and orange zest in a small bowl. Toss lightly and set aside.

Using an electric mixer fitted with a paddle or whisk attachment, whip the egg yolks and ¼ cup sugar on mediumspeed until very pale yellow and about tripled in volume (3-4 minutes). Transfer mixture to a large bowl and set aside.

Wipe out the bowl used to whip the yolks and add the cream and remaining ¼ cup sugar. Whip on medium speed until soft-medium peaks form (about 3-4 minutes). Add mascarpone and continue to whip on medium until you have a soft, spreadable mixture with medium peaks. Gently fold the mascarpone mixture into the egg yolk mixture until combined.

Combine the blood orange juice and Grand Marnier in a shallow bowl and set aside.

Working one at a time, dunk each ladyfinger into the juice mixture for 2-3 seconds per side (don't keep them in too long or they'll get soggy and fall apart). Place them rounded side up at the bottom of the baking dish in an even layer. Repeat, using half the ladyfingers, until the bottom is covered (break any ladyfingers in half as needed to fill in obvious gaps).

Spread half the mascarpone mixture evenly onto the ladyfingers. Repeat with the remaining ladyfingers and mascarpone mixture.

Mash the raspberry mixture with a fork until you have no chunks. Drip the raspberries on top of the mascarpone layer, then swirl the surface using a toothpick.

Cover with plastic wrap and let chill in the refrigerator for at least 4 hours, but ideally 24 hours. Just before serving, top with candied orange slices (if using) and chopped pistachios.