Heat oven to 350. Lay down a lg piece of parchment paper on a lg baking sheet.
In lg bowl,Blend together butter, sugar, egg and vanilla. W/ mixer on low, add flour and baking powder, mix well. Place dough on lightly floured surface. Divide dough into 4 equal parts. Shape each roll 12" long and 3/4"-thick.
Place rolls on baking sheet, 4" apart. Using a wooden spoon handle, make a lengthwise depression in center of each roll, about 4" deep, but not all the way through. Fill depressions w/ jam or preserves. Bake 15-20 min, or until golden. Cut into 3/4" slices.