Preheat oven to 180°C Butter around 20cm cake tin well.
Make the topping first. Combine sugar and the 60mls (1/4 cup) water in a small saucepan and stir over medium heat until sugar dissolves.
Bring to the boil, without stirring, until the syrup turns a golden brown. It is a good idea to occasionally brush down the sides of the saucepan with a pastry brush dipped in water to prevent the syrup from crystallising.
Remove from heat immediately and carefully add the 60mls (1/4 cup) boiling water (the syrup will spit a little when the water is added).
Stir until the toffee is smooth (you may have to return it to the heat to help it dissolve). Pour into the base of the buttered cake tin. Set aside.
Now for the cake. Beat butter and sugar together using an electric beater until pale and creamy. Add eggs and beat until well combined. Mix in the sour cream.
Sift together flour, baking powder, ginger and cinnamon and then fold into the sour cream mixture.
Core, peel and halve the pears and arrange, flat side down, over the toffee in the cake tin. Spoon the cake mixture over the pears and spread evenly.
Bake in pre-heated oven for 50-55 minutes or until cooked through and a skewer inserted into the centre comes out clean.
Stand in tin for 5-10 minutes and then turn onto a serving plate. Serve warm with clotted cream.