Mix the ground flaxseed and water first (= egg replacer) and let it rest a few minutes
In a bowl mix flours, sugar, cream of tartar + baking soda (you can sub these two with 1,5 teaspoon of baking powder), grated lemon zest and a pinch of salt
Add the margarine, the flax-egg and the liqueur
Mix all the ingredients in the bowl with a spoon, then as they start to turn into crumbles, move them on a board and knead the dough until it becomes firm
Shape it into a “ball”, cover it with plastic wrap and refrigerate for at least an hour
Pre-heat the oven at 160°C / 320°F
Put the dough ball on a worktop between two sheets of parchment paper and roll the dough out into a ⅓ inch thick rectangular shape [more or less 13 x 10 inches / 35 x 25 cm]
Peel the apples and cut them into small pieces, in a bowl mix them with all the ingredients for the filling
Remove the piece of parchment paper on top of the rolled out dough
Spread the mix at the center of the shortcrust
Fold close the longer side edges on top (lift the bottom parchment paper to help you push the two long sides together) and then seal close the short-side edges too (with your fingers or pressing down with a fork) , so that the juicy precious filling won't run away while baking
Cover the strudel with a thin layer of jam and some chopped almonds before baking, or leave it as is and dust it with some powdered sugar once it's baked and cooled down
Carefully move the parchment paper with strudel on top to a baking tray and bake for 35 minutes ca., or until it's nice and golden on the bottom and on the top
Once out of the oven, let it cool down, dust with powdered sugar and enjoy!