Cream butter, sugar, and vanilla extract in an electric mixer fitted with the paddle attachment.
Sift together the flour and salt in a separate mixing bowl. With the mixer on low speed, add the flour mixture to the creamed butter and sugar. Mix until the dough starts to come together. Remove and place on a floured worktop and roll together into a flat disk. Wrap in plastic and chill for 1 hour.
Pre-heat oven to 350°F.
Shape dough into 1-inch balls. Place 2 inches apart onto an ungreased cookie sheet. Make indentation in center of each cookie with thumb. Fill each indentation with about 1/4 teaspoon jam.
Bake for 16-20 minutes, or until edges are browned. Let stand 3 minutes on cookie sheets; remove to cooling rack. Cool completely.
Combine all glaze ingredients in bowl with whisk until smooth. Drizzle over cookies.