Line two baking sheets with parchment paper. Preheat oven to 350°F (180°C).
In medium saucepan, combine raspberries, 1/2 cup (125 mL) sugar and lemon juice. Bring to a boil over medium-high heat, stirring constantly to prevent sticking. Boil about 5 min., or until jam has thickened and coats back of spoon. Set aside.
Using electric mixer on medium speed, beat butter and remaining 3/4 cup (175 mL) sugar in large bowl until smooth and creamy, about 1 min. Beat in egg and vanilla extract. Set aside. In separate bowl, stir together flour, baking soda and salt. With mixer on low speed, beat flour mixture into butter mixture until just combined.
Scoop dough into level 1 tbsp (15 mL) portions. Roll into balls. Make 30 balls. Place 2 in. (5 cm) apart on prepared baking sheets. Using your thumb or back of small spoon, make an indent in centre of each cookie. Fill each indent with 1/2 tsp (2 mL) reserved raspberry jam. Bake 15 to 18 min., or until cookies are golden brown at edges and jam is set. Cool on wire rack.
The homemade jam continues to thicken as it cools and again as it bakes on the cookies in the oven. Make blueberry jam by substituting equal parts frozen raspberries with frozen blueberries. Can use prepared jams in place of homemade.