For the crust: Preheat the oven to 190°c. Generously grease an 11-inch tart pan with removable bottom.
Pulse together flour, sugar, and salt. Add butter and pulse until coarse crumbs. Add egg yolk and cream and process until it forms a ball. Wrap in cling wrap and chill 1 hour.
Press dough into bottom of the greased tart dish and up the sides. Poke dough on bottom of the dish all over with a fork to prevent it from puffing up. Press a piece of round parchment paper into the tart and weigh it down with pie weights or uncooked rice.
Bake crust for 15 minutes, then remove the parchment paper with the weights and bake for a few more minutes, until golden brown. Let cool before removing it from the tart dish.
For the lemon filling: While crust is baking, whisk together whole eggs, additional egg yolks, lemon juice, and zest in a medium, heat-proof bowl. In a separate bowl, stir together sugar and potato starch. Once dry ingredients are mixed together, whisk the sugar/starch mixture into bowl with the eggs.
Place the bowl over a simmering pot of water, so it rests on top of the pot. Stir the mixture over medium heat until it thickens, about 10 minutes. Remove bowl from the heat once thickened and stir in the coconut oil or butter right away until it’s fully incorporated and melted in. At this point, pour filling through a fine mesh strainer and into another bowl to remove any lumps.
Once crust is cooled, spread lemon filling evenly into crust, smoothing the top with a spatula. Let pie rest for about 1 hour to allow pie filling to cool and set.
For the blueberry topping: While pie is setting, in a small bowl, combine blueberries, sugar, lemon zest, lemon juice, and lemon liqueur and stir gently but thoroughly to combine. Let stand at least 15 minutes, stirring occasionally, until sugar dissolves and flavours have melded. Refrigerate until ready to serve. May be made up to 1 hour in advance.
When ready to serve, you can either spoon blueberry mixture over entire pie, or place a large spoonful over each slice as you serve it. Can be topped with a dollop of fresh whipped cream, if desired.
