Step 1

Place ¼ cup cold water in a small bowl and evenly sprinkle gelatin over. Let sit until gelatin is softened, 10–12 minutes.

Step 2

Meanwhile, place white chocolate and regular tahini in a medium bowl, then place milk chocolate and black tahini in another medium bowl. Add a pinch of salt to each bowl and set side by side. Bring cream, milk, ¼ cup granulated sugar, and a big pinch of salt to a simmer in a medium saucepan over medium-low heat, whisking to dissolve sugar. Vigorously whisk egg yolks and remaining ¼ cup granulated sugar in a third medium bowl until pale yellow and thick.

Step 3

Remove saucepan from heat and very slowly drizzle about 1 cup hot cream mixture into egg mixture, whisking constantly. Whisk egg mixture into remaining cream mixture in saucepan. Set saucepan over medium heat and cook, whisking constantly, until mixture is thick enough to hold the marks of the whisk, about 3 minutes. Immediately remove from heat and add gelatin mixture; whisk until dissolved.

Step 4

Strain custard through a fine-mesh sieve into a large bowl (you should have about 4 cups), then divide between the 2 bowls filled with tahini and chocolate. (If you have a kitchen scale and want to be exact, measure out 12 oz. custard per bowl.) Let warm custard sit on top 5 minutes so the heat slowly melts the chocolate.

Step 5

Using an immersion blender (or a regular blender), blend white chocolate mixture until smooth and incorporated. Repeat with milk chocolate mixture (no need to wash blender). Cover each one with plastic wrap, pressing directly onto surface and eliminating air bubbles, and chill puddings until set, at least 4 hours.

Step 6

Remove puddings from fridge, uncover, and whisk vigorously until smooth. Transfer each pudding to a piping bag; twist ends of bags to seal and secure with rubber bands. Cut off tips to create about a ½"-wide opening on each bag.

Step 7

Slide both filled bags side by side into a third piping bag. Simultaneously apply slow, even pressure to filled bags to push puddings into third bag in equal amounts so that they are side by side. Slide out filled bags as they empty and you fill the third bag. Once the third bag is about three-quarters full, remove original bags. Twist end of bag with both fillings and secure with a rubber band. Repeat process, emptying original bags into a fourth bag, twist end to close, and secure with a rubber band. Chill bags at least 1 hour to allow pudding to firm up again.Do Ahead: Puddings can be made 3 days ahead. Keep chilled.

Step 8

Beat eggs, egg yolks, and corn syrup in a small bowl with a fork until no streaks remain. Pulse powdered sugar, whole wheat flour, cinnamon, allspice, cloves, nutmeg, kosher salt, and 2¾ cups all-purpose flour in a food processor to combine. Add butter and pulse until largest pieces are the size of a pea. With the motor running, stream in egg mixture; process until dough forms a single mass around the blade.

Step 9

Transfer dough to a work surface and knead a couple of times to work in dry bits. Divide in half and form each into a ½"-thick disk. Wrap in plastic and chill until firm, at least 2 hours.

Step 10

Preheat oven to 350°. Let 1 disk of dough sit at room temperature until slightly softened, about 5 minutes. Roll out between 2 sheets of parchment paper dusted with all-purpose flour until 1/8" thick (dust with more flour as you work if needed). If dough becomes difficult to handle, slide onto a baking sheet (with parchment) and chill a few minutes before proceeding. Using cutter, punch out 6 rounds; save scraps for another use. Working one at a time, firmly press rounds into muffin cups, working into corners and up sides. Press out any creases so pastry is smooth and an even thickness all over. Prick bottoms of crusts in several places with a fork and freeze until firm, 10–15 minutes.

Step 11

Bake crusts, rotating halfway through, until golden brown, 15–20 minutes. Let cool 15 minutes in pan, then turn out onto a wire rack and let cool completely. Repeat process with remaining disk of dough.

Step 12

Scatter halvah across bottoms of crusts. Snip a ¾"-wide opening from tip of fuller bag of puddings. Applying slow, even pressure and twisting top of bag as you go, pipe puddings in a swirl pattern to fill each crust; start at edges and work your way toward the center. When pudding runs out, continue with remaining bag. Sprinkle tarts with sea salt just before serving.Do Ahead: Dough can be made 3 days ahead; keep chilled. Crusts can be baked 1 day ahead; store tightly wrapped at room temperature.