Heat oven to 350°F. Butter a 14-inch rectangular tart pan.
Combine flour and baking powder in a medium bowl and set aside.
Using an electric mixer, cream butter and ½ cup sugar at high speed in a large bowl. Lower speed to medium, add egg, and beat until incorporated.
Gradually add the flour mixture and blend well. The dough will be quite soft.
Press the dough into the pan with floured fingers to form an even crust. Arrange pear halves top to bottom with cut-side down. Sprinkle with the cinnamon and remaining sugar.
Bake until crust is golden brown, about 45 minutes. Let cool.
Warm jam and lemon juice in a small saucepan over medium-low heat, mixing until combined. Remove from heat and brush gently over the entire tart.
Serve with choice of topping, if desired.