1. Preheat oven to 350°F. Spray 11- x 8-inch baking pan with cooking spray.
2. Combine pears, lemon juice, zest, and 1 Tbs. brown sugar in bowl; set aside.
3. Whisk together 3/4 cup brown sugar, sugar, eggs, almond extract, and yogurt in large bowl. Sift in flour, baking powder, salt, and cinnamon, then stir until just combined. Fold in pear mixture. Pour batter into prepared pan, and dot with blackberries. Bake 20 to 25 minutes, or until golden brown and springy on top. Cool 10 minutes on baking rack.
4. Meanwhile, warm jam with 3 Tbs. water in small saucepan over low heat, whisking until smooth.
5. To serve, slice warm cake into 12 pieces. Drizzle each slice with blackberry jam sauce, and garnish with whipped cream (if using).