Beat softened butter with white sugar in a large bowl. Add egg yolk and mix thoroughly.
In a separate bowl, sift together 1 heaping cup flour, salt and mace. Gradually stir flour mixture into butter mixture. The dough should be fairly stiff; you'll need to mix by hand by the end.
Push dough into tart pan, evenly covering the bottom and going up the sides about 1 centimeter.
In a food processor, pulse almonds with remaining flour and 3 tablespoons maple sugar until almonds are finely ground. Evenly coat the bottom of the tart shell with the almond mixture.
Wash the blueberries and pick out any stems and moldy or underripe berries. Scatter the berries over the almond mixture, making sure they do not overlap the crust edge.
Mix the remaining 3 tablespoons sugar with the lemon zest and sprinkle over the blueberries.
Place tart on middle rack of oven and immediately reduce heat to 400. Bake for 30 minutes or until crust is golden brown.
Eat plain or serve with creme freche.
10 inch tart pan