Put 3 cups berries in medium saucepan and cook over medium heat, stirring frequently and mashing occasionally, until berries have broken down and mixture is thickened and reduced to 1 ½ cups, about 8 minutes. Let cool slightly.

Place grated apple in clean kitchen towel and wring dry. Transfer apple to large bowl. Add cooked berries, remaining 3 cups uncooked berries, lemon zest, juice, sugar, tapioca, and salt; toss to combine.

Heat 3 tablespoons of the butter in a large skillet over medium-high. Add the breadcrumbs and cook stirring constantly until golden and toasted. This will take about 3 minutes. Let it cool completely.

Strudel dough

Combine the flour and salt in a stand-mixer fitted with the paddle attachment. Mix the water, oil and vinegar in a measuring cup. Add the water/oil mixture to the flour with the mixer on low speed. You will get a soft dough. Make sure it is not too dry, add a little more water if necessary.

Take the dough out of the mixer. Change to the dough hook. Put the dough ball back in the mixer. Let the dough knead on medium until you get a soft dough ball with a somewhat rough surface.

Take the dough out of the mixer and continue kneading by hand on an unfloured work surface. Knead for about 2 minutes. Pick up the dough and throw it down hard onto your working surface occasionally. Shape the dough into a ball and transfer it to a plate. Oil the top of the dough ball lightly. Cover the ball tightly with plastic wrap. Allow to stand for 30-90 minutes (longer is better).

Put the rack in the upper third of the oven and preheat the oven to 400°F (200°C). Line a large baking sheet with baking paper (parchment paper).

Cover your working area with a pastry cloth, dust it with flour and rub it into the fabric. Divide your dough in to two pieces. Put half of the dough in the middle of the cloth and roll it out as much as you can.

Pick the dough up by holding it by an edge. This way the weight of the dough and gravity can help stretching it as it hangs. Using the back of your hands to gently stretch and pull the dough.

Put it on your work surface. Place your hands underneath the dough and stretch and pull the dough thinner using the backs of your hands. Stretch and pull the dough until it's about 12 inches wide and 18 inches long, it will be tissue-thin by this time. Cut away the thick dough around the edges with scissors if necessary.

The dough is now ready to be filled.

Spread 2 tablespoons of the melted butter over the dough using your hands (a bristle brush could tear the dough, you could use a special feather pastry brush instead of your hands). Sprinkle the buttered dough with the bread crumbs. Spread half of the berry filling about 3 inches from the short edge of the dough.

Fold the short end of the dough onto the filling. Lift the cloth at the short end of the dough so that the strudel rolls onto itself. Transfer the strudel to the prepared baking sheet by lifting it. Tuck the ends under the strudel.

Repeat with the other half of the dough. Brush the tops with the remaining melted butter.

Bake the strudel for about 30 minutes or until it is deep golden brown. Cool for at least 30 minutes before slicing. Use a serrated knife and serve either warm or at room temperature. It is best on the day it is baked.