Heat oven to 350°F. Spray bottom of 8x8-inch baking pan with nonstick cooking spray; line bottom with parchment paper. Spray sides of pan and paper with nonstick cooking spray.
In medium bowl, combine rhubarb, 1/4 cup of the sugar and crystallized ginger; toss to blend.
Melt 4 tablespoons of the butter in medium skillet over medium heat. Add brown sugar; cook until sugar is melted. Spread evenly in bottom of pan; top with rhubarb.
In medium bowl, stir together flour, baking powder, ground ginger, coriander and salt. In large bowl, beat remaining 6 tablespoons butter at medium speed until smooth. Add remaining 2/3 cup sugar; beat 4 to 5 minutes or until light and fluffy.
Alternately stir in milk and remaining flour mixture in two batches, mixing just until combined. Tip: Stirring in remaining milk and flour mixture instead of using an electric mixer makes this cake extra-tender.
Spread batter over rhubarb, pressing with spatula to remove as much air as possible. Tap pan on counter several times to remove air. Bake 40 to 45 minutes or until cake is golden brown, firm to the touch in center and toothpick inserted in center halfway down comes out clean.
Cool on wire rack 10 minutes. Run knife around edges of pan. Invert onto serving platter; carefully remove pan and parchment. Cool completely.
If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.