Using an electric mixer with a paddle attachment, beat the butter on high speed until creamy, about 1 minute.
Turn speed down to medium, and add in the vanilla, sugar, and almond extract. Scrape the sides and bottom of the bowl as needed.
Now turn the mixer off and pour the flour into the wet ingredients. Turn the mixer on low and mix until a very soft dough forms. Compact the dough firmly, and cover it tightly with plastic wrap, then chill it in the refrigerator to make it good and firm–about 4 hours should do it, even longer is fine.
When your dough is good and firm, preheat your oven to 350F degrees.
Line two baking sheets with parchment paper. Form the cookie dough by rolling in in your palms (about one tablespoon at a time) into into smooth, firm, round balls. If the balls are sticky or soft (or both) when you roll them, your dough is not firm enough yet – put the dough back in the refrigerator. Soft dough balls will not work for making Raspberry Almond Thumbprint Cookies.
Once you have your dough all formed into smooth, firm balls, create an indentation into the center of each ball with you thumb. If the dough cracks slightly when you press your thumb into it, just smooth it back out with your fingers – if you can. If there are a few cracks, hey – no big deal.
Now fill all the indentations with enough of the preserves to fill them completely.
Bake your thumb-printed and filled shortbread cookies for about 15 minutes, or until they start browning on the edges and they are puffing up a bit. Do not over-bake them, they will get tough. You could even check on them after 12 or 13 minutes, take them out while they are still a little soft.
Set the cookies aside to cool on the baking sheet for 5 or 6 minutes before transferring them to a wire rack, then let them cool for another half an hour before you glaze them.
Now it’s time to prepare your glaze. Mix all the glazing ingredients together until smooth. Adjust the thickness to your tastes with the amount of milk you add into the mixture.
Drizzle the glaze over the cooled cookies. If you want to get artistic, create a pattern. Let the glazing set up for about 2 hours, and then your Raspberry Almond Thumbprint Cookies are ready to eat.
You can store any that are not eaten right away, covered at room temperature, for up to 3 days. Raspberry Almond Thumbprint Cookies will stay good in the refrigerator for a full week.