Filling: In a heavy bottom medium saucepan add 4 pints blueberries, the sugar, and the lemon juice. Coarsely mash the berries with a fork. Stir over medium-high heat until the sugar dissolves and mixture boils and thickens, about 8 minutes. In a medium bowl whisk the egg yolks and cornstarch together. Slowly whisk in half of the hot berry mixture (making sure not to cook egg yolks), then return the egg mixture to the pan. Stir over medium-high heat until mixture boils and thickens, about 3 minutes. Whisk in the butter, and lemon peel. Transfer the filling to a bowl, cover and refrigerate overnight.
Crust: Mix the flour, 1/3 cup sliced almonds, sugar, and salt in a food processor until the almonds are finely ground. Add the butter, pulsing until the mixture looks like coarse meal. In a small bowl, whisk together the egg yolk, and almond extract. Add the mixture to the food processor and blend until moist clumps form. Gather the dough into a ball and flatten it into a disk. Lightly butter a 9-inch-diameter tart pan with a removable bottom. Press the dough onto the bottom and up the sides of the pan. Pierce the crust all over with fork, and freeze for 45 minutes.
Preheat the oven to 350 degree F. Line the crust with foil, and fill it with dried beans or pie weights.
Bake until the crust is set, about 12 minutes. Remove the foil and beans, and continue to bake until the crust is golden, about 16 minutes more. Cool the crust completely on a rack. Spread the filling in the crust, and sprinkle the remaining 1 1/4 pints of blueberries over the filling. In a small saucepan over medium heat, add the black currant jelly and stir until melted. Brush the jelly over the berries as a glaze. Sprinkle the remaining 2 tablespoons sliced almonds around the edge of the tart. Cover loosely with foil and chill at least 2 hours. Remove the pan sides. Put the tart on a platter, and serve cold or at room temperature.