FOR THE PASTRY: Combine pastry ingredients by hand or in a food processor to form a soft dough - Do not overmix.
Roll out and line an 11-or-12-inch pie or tart pan; prick the base and chill for 15-to-20 minutes.
FOR THE FILLING: Heat 1/3 of the butter in a saute pan, add the chopped almonds and saute over medium heat until browned; cool.
Melt the remaining butter in a small saucepan; cool.
Mix the ground almonds and sugar in a bowl and add the eggs one by one, beating after each addition until the mixture is light and thick.
Sift the cornstarch (or potato starch) with the baking powder and salt and fold into the almond mixture; fold in the melted butter - Do not overmix.
Pour the mixture into the tart shell and bake for 10-12 minutes or until the batter begins to set.
Quickly scatter the chopped almonds over the top in one even layer.
Return the tart to the oven and continue baking for 17-to-20 minutes or until the pastry is brown and the filling is firm.