In the bowl of an electric mixer, beat the butter and sugar together until light and fluffy, scraping down the bowl as necessary. Add the egg yolks, beat in well, and add the almond extract. Remove the beater and stir in the ground almonds and flour until evenly blended. the mixture should be the consistency of a thick paste.
Preheat the oven to 400 degrees. On a lightly floured surface, roll out the pastry to a 1/8-inch thickness and, using a plate or cardboard circle as a template, use a very sharp knife to cut four 7-inch circles. Spread a circle of frangipane (they should be touching each other so that you can fit as many as possible onto the circle of frangipane). Beat the egg yolk lightly with a fork and brush the border of the pastry with it (try not to let any yolk dribble down onto the cut edges of the pastry, otherwise it will not rise as high). Bake the tarts for about 20 minutes, until the edges are golden and the pastry is baked through. Remove from the oven and allow to cool for 5 minutes. Place a sprig of mint in the center of each tart and sprinkle it lightly with confectioners' sugar. Serve while still warm, accompanied by a scoop of vanilla ice cream