Preheat the oven to 350°F (170°C or 160°C for fan/convection ovens).
Grease the bottom and sides of an 8 inch (21cm) loose-bottomed cake pan.
Peel the pears, one at a time. Chop the first pear and put it in a small bowl. Toss the chopped pear pieces in half the lemon juice to prevent them turning brown. Cut the remaining pears into slices, and place in another small bowl. Add the remaining lemon juice to this bowl and toss the pear slices gently so they remain intact. Set both bowls aside.
Using an electric mixer, cream the butter and sugar together.
Add the eggs and almond flavouring and beat for a minute or so.
Sift together the flour, baking powder, ginger, nutmeg and salt.
Add the flour mixture to the batter and mix well.
Pour in the buttermilk and beat until the cake mixture is smooth.
Gently fold in the chopped pear only.
Pour the batter into the prepared cake pan, smoothing the top.
Arrange the sliced pears on top of the cake in a circular fashion. Don't get stressed about this, it doesn't need to be perfect!
Sprinkle the top of the cake with the Demerera sugar.
Bake for 30 to 35 minutes, until a skewer inserted in the centre of the cake comes out clean and the top of the cake is beginning to turn golden.
Remove the cake from the oven and cool on a wire rack for at least 30 minutes.
When the cake pan is cool enough to handle, release the springs and gently remove the sides. You can leave the cake on the metal base of the cake pan to serve it. (However, if you are feeling brave, you can remove it by sliding a knife very carefully between the cake and the metal base. Use a large slice or egg lifter to transfer it to the wire rack to cool completely.)
When the cake is completely cool, it's ready to glaze. Put the icing sugar in a bowl and gradually add the water, a bit at a time, until a smooth, drizzle-able consistency is reached.
Drizzle the glaze over the cake.
Let the glaze set before slicing the cake.