Firstly make the filling: Mix together the brown sugar and cinnamon for the filling and set aside.

Next, make the streusel topping: In a bowl stir together the flour, sugar and cinnamon. Rub in the margarine with your fingertips to make a crumble like consistency. Set aside.

Preheat the oven to 180 degrees centigrade. Grease and line a spring-form cake tin

Sift together the flour, custard powder or corn flour and bicarbonate and set aside

In another bowl, mix together the yogurt, oat milk and vanilla and set aside

Cream together the margarine and sugar until light and fluffy

Alternately add the flour and yogurt mix (about 1/3rd of the mix each time) and stir well between each addition.

Pour 1/3rd of the mix into the cake tin and level off.

Sprinkle over 1/2 the cinnamon/sugar mix on top, then repeat with two more layers of batter and one of cinnamon sugar.

Scatter over the streusel mixture and then bake for 35-40 minutes, until a knife cones out clean

Cool briefly in the tin before unmoulding and cooling on a wire rack.