Gently heat the ground almonds for the filling in a small frying pan,stirring often, for 1-2 minutes to lightly brown.Cool. rub the flour & diced, chilled butter together with your fingers to make fine crumbs.Stir in 1 tbsp of icing sugar,then the yolk, then gradually add 3 tbsp cold water or enough so that the dough comes together.Gather it into a ball.
Roll the pastry on to a lightly floured surface & use to line a 4cm deep 20cm fluted flan tin,fitting the pastry into each flute so that it does not shrink during baking. Chill for 1 hour.
Heat oven to 200c/fan 18oc/gas 6. Line the pastry with greaseproof paper & baking beans & bake for 12 minutes, then remove paper & beans & bake for a further 5 minutes. Lower the heat to 180c/fan160c/gas4. Cream the butter & sugar for the filling with a electric whisk until light & creamy. Gradually add teh eggs, beating well after each addition - the mixture will look curdled.Lightly fold in the ground almonds & almond essence.
Spread jam over the base of the pastry.Pour over the almond filling, sprinkle with almonds & bake for 25-30 minutes until pale golden. Cool slightly. to make the icing,sift the sugar into a bowl& stir in a few drops of cold water to make a thickish consistency. Drizzle it over the tart, allow to set.