Preheat oven to 350 degrees. Coat an 8-inch square or round cake pan with cooking spray. Line bottom with parchment paper, and set aside.
Pulse saffron and 1/4 cup sugar in a spice grinder until well combined. Put butter and saffron sugar into the bowl of an electric mixer fitted with the paddle attachment. Mix on medium-high speed until pale and fluffy, about 3 minutes. Using a small offset spatula, spread mixture into prepared pan.
Peel pears; halve lengthwise, and core. Using a mandoline or a very sharp knife, cut pears lengthwise into 1/4-inch-thick slices. Arrange pears decoratively in pan over saffron-butter mixture.
Whisk together flour, remaining 3/4 cup sugar, the baking powder, ground ginger, and salt in a large bowl. Whisk buttermilk, oil, eggs, and vanilla in another bowl. Add buttermilk mixture to flour mixture in a slow, steady stream, whisking. Stir in crystallized ginger.
Spread batter over pears. Bake until set and a cake tester inserted into center comes out clean, 40 to 45 minutes. Let cool 5 minutes. Place a serving platter upside down over pan; flip to unmold cake. Peel off parchment.
This cake is so incredible. I was not at all prepared for how it would taste. The candied ginger melts right into the batter as it bakes it's moist and buttery and delicately flavored. STUNNING! Making this one for thanksgiving!