Sift the flour, sugar, baking powder and salt together into a bowl. Add the butter, egg yolk, and lemon zest and work the ingredients together with your fingers until the butter resembles cornflakes and is distributed evenly throughout the flour mixture. Sprinkle 3 tablespoons ice water over the mixture and toss lightly just until the dough holds together when lightly pressed. If necessary, add a little more ice water. Wrap the dough in plastic wrap and let rest in the refrigerator for 1 hour.

Butter a 10 inch tart pan with a removable bottom. Roll out the dough to a 12-inch circle of even thickness. Center the dough over the tart pan, fit the dough well into the edges with your fingers, and trim off excess overhanging dough. Prick the bottom of the tart shell with a fork, and set on a baking sheet in the freezer for 10 minutes.

Meanwhile, preheat the oven to 350 degrees F.

Make the filling: with an electric mixer at medium speed, cream the butter with the sugar until fluffy, about 3 minutes. Add the eggs one at a time, beating well after each addition. Add the almond flour and vanilla mix until a smooth batter forms.

Brush the tart shell with 1/4 cup of apricot glaze, then spread the blueberries over the bottom. Pour the almond mixture over the blueberries, and with a spatula, spread it evenly. Arrange the apricot halves over the almond mixture, cut side down. Place the tart in the oven and bake until the almond mixture and the edges of the tart shell are golden brown, about 40 minutes.

Let the tart cool for 30 minutes, then brush with the remaining 1/4 cup warm apricot glaze. (You can buy apricot glaze, but to make your own, warm apricot jam in a small saucepan over low heat. If the jam is chunky, add a tablespoon or two of water and strain before using.)