Preheat oven to 375F..toast nuts in oven for 3 to 4 minutes and stir them and watch so as not to burn remove from oven let cool and chop very fine. In a bowl add the flour, nuts and brown sugar and mix together..add the butter and using a pastry blender or 2 forks combine these all together..whisk the egg yolk with the ice water and drizzle over flour mix,toss to combine press into greased tart cups or use muffin tin,,,press into bottom and up the side of 12 baking foil cups or muffin pans., bake 10 minutes or until golden. cool completely.
Filling..in heat proof metal or glass bowl over a pot of simmering water whisk the egg yolks with the lemon juice and zest and sugar for about 10 minutes whisking all the time until very thick remove off pot of water in whisk in the butter..with wax paper. Keep coveron the egg mix so it touches and cool in the refrigerator...divide filling evenly into prepared containers. serve with a dollop of whipping cream.