Cream room temperature butter with ½ cup sugar for two minutes, so the mixture becomes light and fluffy. Feel free to occasionally scrape the sides of the bowl with a rubber spatula as needed.
Add in the egg yolk and almond extract, beat to combine for about 30 seconds.
Add in half the flour and beat until combined (about 20 seconds) then add in the last half of the flour and beat until the dough comes together but is still a bit crumbly looking (about another 30 seconds).
Take about a tablespoon dough (19-20g) and roll it into a ball. Roll the dough ball in a small bowl of granulated sugar. Place the ball on a parchment paper-lined baking sheet and press your thumb in the middle to make a thumbprint divot. The cookies don’t spread much during cooking but make sure there is room for air circulation between the cookies.
Once all the dough balls are prepared, cover with plastic wrap and place the baking sheet into the fridge to chill for 1 hour or into the freezer for 30 minutes.
Preheat oven to 350F
After the cookies have chilled, fill the divots with raspberry jam (or your preferred flavor) and place the baking sheet in the oven for 17-20 minutes. The cookies will be very lightly browned around the edges. Pull the pan out of the oven and allow the cookies to cool for about 5 minutes and then remove them to a cooling rack to completely cool.
Once cookies have cooled you can serve them or you can glaze them if you like.
Make the glaze
While cookies are cooling make the glaze.
To the bowl of confectioner’s sugar, add all the vanilla extract and 1 tablespoon of milk or water. Stir to combine. Depending on the consistency you want, you may be happy as is, or you can add a little more liquid to make it a bit thinner. I recommend just adding about ¼ teaspoon at a time and mixing in.
Place icing sugar in a piping bag with a small tip or you can place in a small zipper top bag as I did in these pictures. If using a zipper top bag, just cut a very small bit of the corner off to pipe out of.
Pipe icing over the cookies in any pattern you like.