Step 1

Preheat oven to 350°F. In bowl, beat butter and sugar with electric mixer on medium-high heat speed until pale and fluffy, 3 to 4 minutes. Add egg, and beat until completely combined. Reduce speed to low, add flour, and mix just until incorporated.

Step 2

Shape dough into 1-inch balls. Place on parchment-lined baking sheets, spacing at least 3 inches apart.

Step 3

Moisten thumb with water, and gently press center of each ball to make indentation. Heat jam in small saucepan over medium until melted; spoon about 1/2 teaspoon into each indentation. Bake, rotating sheet halfway through, until cookies are golden brown around edges, 18 to 20 minutes. Transfer to a wire rack, and let cool completely. Cookies can be stored in single layers in an airtight container at room temperature up to 2 days.