Heat oven to 350 degrees. Butter a 9-inch-square cake pan; set aside. In a large bowl, toss pears with lemon juice. In a large skillet over medium-high heat, melt 2 tablespoons butter; sprinkle with 2 tablespoons granulated sugar. Add half the pears, cut sides down, in single layer; cook until brown, 2 to 3 minutes. Turn pears over; cook other sides until brown, 2 to 3 minutes. Using a slotted spoon, transfer cooked pears to a plate. Cook remaining pears; transfer to plate. To pear juices in skillet, add brandy, and sprinkle with remaining 2 tablespoons granulated sugar. Cook, stirring, until reduced to syrup, about 1 minute. Pour into cake pan; swirl to spread. Starting in one corner of pan, fan out pears in single layer; arrange so the tapered sides lie in same direction. Set aside.
In a medium bowl, whisk together flour, ground ginger, cinnamon, cloves, nutmeg, and salt; set aside. In bowl of an electric mixer, beat remaining 8 tablespoons butter until fluffy. Add brown sugar; beat on medium-high speed for 3 minutes. Add eggs; beat to combine. Beat in molasses and grated ginger.
Add half of flour mixture; combine on low speed. In a small bowl, combine baking soda and boiling water; beat into batter. Beat in remaining flour mixture until combined. Pour into pan; bake 25 minutes. Reduce heat to 325 degrees. bake until springy to the touch, 15 to 20 minutes. Cool on a wire rack for 1 hour. Run a knife between pan and cake. Invert cake onto a serving plate. Arrange pears as needed, and serve.