To make tart shells, pour fennel seeds into a small nonstick skillet and toast over medium heat until browned and fragrant, 2 to 3 minutes. Pour onto a plate to cool.
Sift together flours, salt, cinnamon, and baking soda.
Combine butter, sugars, and vanilla in bowl of a stand mixer with the paddle attachment. Cream on medium speed until light and fluffy.
Add honey and mix on medium speed until combined. Add egg yolk and mix on low speed until fully combined.
With mixer on low, gradually add dry ingredients and mix just until a dough forms. Scrape bowl and beater and mix once more to incorporate everything fully.
Set aside 1/2 tsp. toasted fennel seeds. Mix remaining seeds into dough.
Place a large piece of plastic wrap onto a work surface, turn dough out onto plastic, form into a ball, and wrap up in plastic. Chill until firm, at least 45 minutes. Meanwhile, preheat oven to 325°.
On a well-floured work surface, roll dough out until about 1/8 in. thick (flouring pin and top of dough as needed). Using a 41/2-in. biscuit cutter or a knife, cut out 8 circles, re-rolling dough if needed (but no more than twice). Spray 8 (4-in.) fluted tart pans with nonstick baking spray.
Gently ease each circle of dough into a tart pan and press gently into grooves, trimming dough even with rim using a paring knife. Set pans on a baking sheet. Prick bottoms of shells several times each with a fork.
Bake shells 15 to 18 minutes, or until browned and crisp-looking. Let cool slightly on a rack, 15 minutes, and then gently unmold.
To make lime curd, pour enough water into a pot to come 1 in. up side. Bring to a simmer over medium heat.
Meanwhile, place a metal bowl that will nest into pot without touching water. Add to bowl sugar with egg yolks, then vigorously whisk until a shade paler, about 1 minute. Whisk in whole eggs, lime juice, and lime zest. Set bowl over simmering water and cook, whisking gently, until thick enough that the whisk leaves tracks, about 5 minutes.
Remove bowl from heat and whisk in butter a few pieces at a time. Strain lime curd into a shallow bowl and set in a bowl of ice water. When cooled, cover with plastic wrap, pressing wrap against surface of curd. Chill until cold, at least 1 hour.
Fill each baked tart shell with about 1/4 cup lime curd and chill at least 20 minutes and up to 1 day (cover, with wrap lying against surface of curd, if chilling longer than an hour).
To make orange blossom cream, whip cream and sugar in a medium bowl on medium speed until soft peaks form. Add orange blossom water and turmeric and whip on low speed just until stiff peaks form.
Top tarts with orange blossom cream just before serving (about 2 tbsp. per tart). Sprinkle with lime zest, along with remaining 1/2 tsp. toasted fennel seeds.
MAKE AHEAD Tart shells: Up to 2 days, cooled and stored airtight at room temperature. Lime curd: Up to 2 weeks, chilled, with plastic wrap pressed against surface. Tarts filled through step 14: Up to
1 day, covered and chilled. Orange blossom cream: Up to 4 hours, chilled.
*Graham flour is whole-milled whole-wheat flour; we like Bob’s Red Mill brand. If you can’t find it, use regular whole-wheat flour (the crusts may be a little drier, though).