Measure three-quarters of the milk into a saucepan, add the cinnamon, cardamom, nutmeg and heat to just below boiling point. Set aside to infuse for about 15 minutes.
Mix together the remaining milk, egg yolks, flour,cornstarch, sugar and baking powder. Strain the spiced-flavoured milk, pour into a clean saucepan and cook, stirring, until the custard thickens. Remove from the heat, and whisk in the butter and vanilla. Cool to room temperature.
Whisk the egg white stiffly and fold into the custard. Pour into the pastry shell and bake in a preheated oven at 375°F and bake for about 20 minutes more, until the filling is set. Slide the hot tart onto a plate, sprinkle with ground cinnamon whipped cream and serve warm or chill to serve cold.