In a large bowl, beat at medium speed sugar, butter, egg, and vanilla until creamy. (It will take a few minutes for dough to come together.) 

Lower speed and add in flour and baking powder, beating until combined.

Chill for 1 hour, to prevent dough from spreading too much when baked. 

Just before removing dough from refrigerator, preheat oven to 350°F and line two baking sheets with parchment paper. Set aside. 

Then, combine all filling ingredients in a bowl, mixing well.

Remove dough from fridge. Roll dough into 1 1/4-inch balls, placing the balls 2 inches apart on the cookie sheet.

Using your thumb, make an indentation in the center of each cookie, rotating your thumb to deepen and widen the indentation slightly.

Fill each cookie - indentation with 1 teaspoon of filling. I made all the cookies at once (using parchment paper on the counter for those that didn't fit on my cookie sheet) so that if there was extra filling, I could spread it around.

Bake for 8-12 minutes, until lightly browned.

Let sit on cookie sheets for a minute or two before transferring to a cooling rack to cool completely. Store in an airtight container at room temperature.