Preheat oven to Gas Mark 4/175°C/350°F and grease and line a 20cm cake tin.
Sift together flour, baking powder and spices and set aside.
Cream together the softened butter and 220g of sugar until light and fluffy. Beat in the eggs, one at a time, then fold in the flour mixture and ground almonds until everything is combined.
Spoon into prepared cake tin and level off the top.
Cut pears into quarters and remove the cores. Thinly slice each quarter, and arrange the slices over the top of the cake. Make sure that each slice overlaps slightly.
Sprinkle the top with the extra caster sugar.
Bake for about 1 hour, or until a skewer inserted into the centre comes out clean.
Leave to cool in the tin for 10 minutes before turning cake out into a wire rack to cool.
Meanwhile, make the butterscotch sauce:
Add brown sugar, butter, cream, and vanilla to a pan. Place pan over a medium heat and stir until the butter melts and the sugar dissolves. Bring to a gentle simmer and cook for around five mintutes, stirring occasionally, until the mixture thickens slightly. Remove from the heat and let cool slightly. Taste and tweak, adding salt and more vanilla if needed!