Preheat the oven to 180 C (350 F).
Line bottom of the 23 cm (9inch) springform pan with baking paper, butter and flour the edges of the pan.
Make ginger crumb topping: Mix sugar, flour, cinnamon and candied ginger together in a bowl, then stir in melted butter. Put the topping in the freezer while you mix up the cake.
In a bowl gently coat pears with 1-2 tablespoons flour.
Whisk flour, cornstarch, baking powder, ginger, cinnamon and salt in a bowl. Using an handheld mixer (or stand mixer with paddle attachment), cream the butter and sugars together on medium-high speed until fluffy, 3-4 minutes. Add in the eggs, one at a time, scraping down sides of bowl after each addition. Beat in vanilla extract.
Stir in the flour mixture in three additions, alternating with yogurt in two additions, beginning and ending with dry ingredients, and scraping down the sides of the bowl occasionally. Do not over mix! Gently fold in pears.
Spread the batter into the prepared pan, then sprinkle the crumb topping over the cake—make sure the crumb is totally frozen, and that you move quickly to sprinkle it over the cake and transfer to the oven.
Bake until a wooden pick inserted in center comes out clean, about 50 minutes, covering with foil to prevent excess browning, if necessary. I suggest that you do the skewer test at approx 45 min and every 5 minutes after that up until the skewer comes out clean meaning the cake is ready.