Preheat oven to 350 degrees
In the bowl of a stand mixer with a paddle attachment, on medium-high speed, cream the butter and brown sugar until light and fluffy (2 minutes)
Add the egg yolks and vanilla until well blended
Work in the flour and salt until it holds together
Grease a 9X9 pan or line with parchment paper
Add the cookie dough to the pan and spread evenly, pressing down with your palm to smooth the top out
Using your thumb or the back of a small spoon, make indentations into the top, four across in three rows, or for larger bars, three across in three rows
Spoon jelly to each indention only to the top or it will bubble over
Bake in oven at 350 degrees for about 30 minutes, or until golden brown. It's better to have them feel a bit underdone than too brown.
Glaze
Whisk powdered sugar and milk together in a small bowl until smooth. Depending on how thick you'd like it add more or less milk.
Drizzle powdered sugar mixture over the top of the bars.
Cut into even squares with the jelly filling in the middle of each square.