Preheat the oven to 180°C/160℃ fan/350°F/gas mark 4. Line a deep 20 cm (8 in) square cake tin with baking paper, making sure that you leave some overhanging on either side so that you can easily lift the cake out later.
To make the streusel topping, mix the flour, sugar and cinnamon together in a bowl. Add the butter and rub it in using your fingertips until no lumps of butter remain. Place in the fridge.
100 g (¾ cup + 1 Tablespoon) plain (all-purpose) flour, 50 g (¼ cup) light brown soft sugar, ½ teaspoon ground cinnamon, 70 g (5 Tablespoons) vegan block butter
To make the strawberry topping, hull the strawberries and cut them into quarters (or halves if very small/sixes if very big). Toss them with the sugar and cornflour until they are well coated. Set aside.
400-450 g (3 cups) fresh strawberries, 1 Tablespoon caster or granulated sugar, 2 Tablespoons cornflour (cornstarch)
To make the cake batter, whisk together the yogurt, milk, oil, vinegar, caster sugar and vanilla extract in a large bowl until very well combined.
135 g (½ cup + 1 Tablespoon) vegan Greek style yogurt, 120 g (½ cup) unsweetened non-dairy milk (I use soy), 82 g (90ml/6 Tablespoons) neutral oil (I use olive), 1 teaspoon vinegar, 150 g (¾ cup) caster or granulated sugar, 1 Tablespoon vanilla extract
Whisk in the cornflour, baking powder and soda and salt then add the plain flour and gently stir with a balloon whisk until no dry lumps remain.
20 g (2 packed Tablespoons) cornflour (cornstarch), 1 ½ teaspoons baking powder, ½ teaspoon bicarbonate of soda (baking soda), ¼ teaspoon salt, 225 g (1 ¾ cups + 6 teaspoons) plain (all-purpose) flour
Pour the batter into the prepared tin and spread it level. Scatter over the strawberries in an even layer. Sprinkle the crumb mixture on top.
Bake for about 60 minutes until a skewer inserted into the centre comes out clean or with a few crumbs but no wet batter. Loosely cover the cake with tin foil after 45 minutes or so if the top starts to darken too much.
Leave the cake to cool in the tin for 20 minutes then use the overhanging baking paper to carefully lift it out of the tin onto a wire cooling rack. Leave to cool completely before slicing. Best eaten on the day it is baked.