BAeat the butter and both sugars together using an electric whisk for 6-8 mins, or until light and fluffy. Add the eggs, one at a time, beating well after each addition, then mix in the soured cream. Add all the dry ingredients and beat for 10 seconds to incorporate. Spoon the cake mixture over the pears, gently smooth the surface, then bake for 1 hr until a skewer inserted into the middle comes out clean. If any wet crumbs cling to the skewer, bake for a further 5-10 mins. Leave to cool completely in the tin, then invert onto a serving plate and remove the parchment before slicing.
