Beat the butter and powdered sugar in the bowl of a stand mixer until creamy.
Beat in the egg yolk and mix until fully combined.
With the mixer on low speed, beat in the salt and flour just until the dough comes together and there is no more visible flour. Careful not to overmix. Remove dough from the bowl and press the dough into the tart pan, making sure it is evenly distributed. Using a fork, prick the bottom of the tart shell to prevent the bottom from puffing up when baking.
Wrap the pan loosely in plastic and chill 30 minutes.
Bake the tart shell at 350F or until the crust is a light golden brown (approximately 13 minutes). Remove carefully from oven and let rest on a wire rack.
In a stand mixer fitted with the whisk attachment, whip the tahini on high speed for 5 minutes, until slightly thickened.
Gradually add the sugar and beat to combine.
Scrape down the sides of the bowl and whisk again—all of the sugar should be dissolved (and no longer visible).
Add the butter, piece by piece, scraping down the sides of the bowl, until fully incorporated. [Note: I found that adding 2 additional tablespoons of butter was helpful, especially if the brand of tahini you have on hand is on the drier side]
Add the egg and salt and beat until well combined.
With an offset spatula, evenly spread out the tahini frangipane in the tart crust.
Quarter and core the apples, then thinly slice the apple quarters. Fan them out on top of tahini layer before baking.
Bake the tart for 35 to 40 minutes, rotating halfway through, until the crust is a deep golden-brown. If the apples are browning too quickly, place a piece of aluminum foil loosely on top.
Place hibiscus in small saucepan with 1 cup of water. Simmer until the hibiscus has imparted a deep pink colour. Strain through a fine mesh sieve.
Return the liquid back to the pot, then add the honey, lemon juice, sugar, and a pinch of salt.
Bring to a simmer and reduce, stirring very frequently with a rubber spatula, until thick and syrupy.
Hibiscus Apple Tahini Frangipane Tart by Amy of Constellation Inspiration