Preheat the oven to 350 degrees Fahrenheit and grease a 9x13-inch baking pan.
Make the streusel by combining the flour, brown sugar, cinnamon, ginger, cardamom, nutmeg, and cloves, then cut in the butter with a pastry cutter, fork, or your fingers until crumbly.
To make the cake, whisk together the flour, baking powder, cinnamon, baking soda, ginger, salt, cardamom, nutmeg, and cloves in a large bowl.
In another bowl, beat the sugar and butter until light and fluffy, then beat in the eggs and vanilla.
Mix in the sour cream, then gradually add the dry ingredients until just combined.
Gently fold in the diced pears.
Spread the batter into the prepared pan and sprinkle evenly with the streusel topping.
Bake for 45-50 minutes, or until a toothpick inserted in the center comes out clean.
Cool slightly before slicing and serving with a dusting of powdered sugar if desired.