Preheat the oven to 350°. Line a baking sheet with parchment paper or a silicone baking mat.
In the bowl of a food processor, combine butter and brown sugar. Pulse until blended. Add vanilla and egg yolk. Blend until smooth.
½ cup butter, ⅓ cup brown sugar, ¾ teaspoon vanilla extract, 1 egg yolk
Add flour, oats, and salt. Pulse until blended.
1 cup unbleached, all-purpose flour, ½ cup rolled oats, ⅛ teaspoon salt
Roll dough into 18 walnut-sized balls. Arrange on a baking sheet, about 2 inches apart. Press your thumb into the center of each cookie, making a depression. Make a fairly deep well as the cookie may flatten a bit while baking.
Bake for 10 minutes. Remove the pan from the oven. Fill depressions with small spoonful of the jam.
½ cup raspberry jam
Bake for another 10 minutes or until golden. Cool the cookies on a wire rack.
Notes
Nutritional values are approximate and based on 1 cookie.Store the cookies in an airtight container for 4 days. Freeze for longer storage.Variation: For Raspberry Almond Thumbprints, swap the oats out for finely chopped almonds. Use ½ teaspoon almond extract instead of vanilla.