Preheat oven to 350 degrees F.
In a stand mixer or with a hand mixer, with a paddle attachment on medium speed, cream together the butter and sugar until light and fluffy, about 3 minutes.
With the speed on low, add the almond meal followed by the lightly beaten egg and almond extract.
Scrape the sides of the bowl and add the flour and baking powder.
Mix together, with a wooden spoon until fully incorporated. Do not overmix the dough.
Roll 1-inch balls of dough and place on a parchment-lined baking sheet until all of the shortbread dough has been used.
Gently coat each ball in the egg white and then roll the balls in the crushed almonds.
Divide the balls between 2 parchment-lined baking sheet, about 15 per sheet. Using your thumb, gently press down into the center of each ball, creating a "thumbprint" in the cookie dough.
Place the baking sheets into a refrigerator and allow the cookie balls to chill for about 30 minutes
Remove the baking sheet from the refrigerator, place it in the oven and bake for 16 to 20 minutes or until the tops of the cookies just begin to brown.
Remove from the oven and allow the cookies to cool.
While the cookies cool, begin making the caramel by combining the granulated sugar, brown sugar, and corn syrup in a medium sauce pan. Bring the mixture to a boil on medium-high heat.
Once the mixture reaches 240 degrees F on a candy thermometer remove from the heat and whisk in the butter, cream, and evaporated milk until fully incorporated.
Stir in the vanilla and allow the hot caramel to cool slightly, about 15 minutes.
Place 1 to 2 teaspoons of the warm caramel into each thumbprint (depending on the size of the thumbprint indentation) on each cookie.
Once all of the cookies have been filled, allow the caramel to set, about 1 hour.
Sprinkle the tops of each cookie with the sea salt flakes and serve or store in an airtight container.
Be careful, the mixture will begin to bubble violently.
Recipe courtesy of Matt Armendariz