For water crackers, preheat oven to 150C. Combine flour and baking powder in a bowl and make a well in the centre. Add oil and 160ml water to well, mix until a soft dough forms. Turn onto a lightly floured surface, knead lightly until mixture just comes together. Divide in thirds, form each into a ball, flatten slightly, wrap loosely in plastic wrap, rest for 20 minutes. Roll each piece of dough to 1mm thick, brush with eggwhite and scatter with pepper. Cut into rough 2cm x 10cm rectangles with a lightly floured sharp knife and place on baking trays lined with baking paper. Bake in batches until light golden on edges (10-15 minutes), then transfer to a wire rack until cool. Makes about 50. Water crackers will keep stored in an airtight container for 1 week.
Place cod roe in a non-reactive bowl, cover with water, soak to remove salt (30 minutes), drain. Place bread in a separate bowl, cover with water, soak until softened (15 minutes), drain, squeeze out excess water. Process roe, bread, onion and garlic in a food processor to combine. With motor running, add oil in a thin steady stream and process until thick and emulsified. Season with pepper and lemon juice, refrigerate until required. Makes about 500ml. Taramasalata will keep refrigerated in an airtight container for 1 week. Serve with black pepper water crackers and salmon roe.