Preheat the oven to 180 degrees Celsius (350 Fahrenheit) and grease a 23cm spring form tin.
Place the rhubarb, sugar, water and ginger in a small saucepan and cover with a lid. Bring to a simmer over a low heat and cook until the rhubarb is tender, about 5 minutes. Remove from the heat and remove the lid and leave to cool.
To prepare the crumble topping sift the flour, baking powder into the bowl of a mixer fitter with a paddle attachment. Add the butter and sugar and set the mix to it's lowest speed and mix until the mixture resembles breadcrumbs. Place in the refrigerator while you make the cake.
To make the cake batter, cream the butter and sugar until light and fluffy. Add the eggs, one at a time, and mix to combine before adding the milk and ginger. Then sift over the flour, salt and baking powder and fold into the cake batter.
Spoon the cake batter into the prepared spring form tin and spread out evenly before topping with the cooked rhubarb along with the liquid. Finally top with the crumble topping and finally the flaked almonds.
Bake for 45 minutes, or until golden and cooked in the center. Cool in the tin slightly before removing.