Start by making the pastry dough. On a clean countertop or large board, combine the flour and the cubed butter. Using your fingertips, gently rub the butter into the flour until the mixture resembles coarse crumbs—kind of like sand with little bits of butter throughout.
Add the egg yolk to the crumbly mix and gently bring everything together by kneading just enough until it forms a smooth dough. Be careful not to over-knead, as you want the pastry to stay tender and flaky. Shape the dough into a flat disc, wrap it tightly in cling film, and pop it into the fridge for at least half an hour to rest.
While the dough chills, prepare your apples. Peel and core the cooking apples first, then slice them thinly—try to keep the slices even for a nice look. Toss these apple slices with fresh lemon juice to keep them from turning brown. Next, peel and slice the dessert apples; these will go on top later for a beautiful presentation.
Heat your oven to 375°F (190°C) so it’s ready when the tart is assembled.
Take the chilled dough and lightly flour your work surface. Roll it out evenly until it’s large enough to line a 9-inch (23 cm) tart tin. Carefully lift the dough and press it into the tin, making sure it fits snugly around the edges. Trim any extra dough hanging over the sides. Use a fork to prick holes all over the base—this helps stop any puffing while baking.
Melt the salted butter and brush a thin layer over the pastry base; this adds flavor and helps keep the crust moist.
Neatly arrange the cooking apple slices across the base of the tart, covering it completely. Sprinkle the sugar evenly on top and scatter the lemon zest for a fresh, citrusy aroma. Dot small pieces of butter across the apples for extra richness as they bake.
Bake the tart for about 30 minutes. During this time, the apples will start to soften and the pastry will begin to turn golden.
After 30 minutes, take the tart out and carefully arrange the dessert apple slices on top in a pretty, decorative pattern. Pop the tart back in the oven for another 20 minutes or until the apples are tender and the crust is beautifully golden brown.
While the tart cools slightly, warm the apricot jam gently—either in a small saucepan over low heat or in short bursts in the microwave—until it becomes smooth and runny.
Use a pastry brush to glaze the warm tart with the apricot jam. This gives the tart a shiny, appetizing finish.
Let the tart cool for a few minutes before slicing and serving. Enjoy your beautiful, homemade French Apple Tart!