In a large bowl or the bowl of a stand mixer, beat 1 cup butter and 2/3 cup granulated sugar on a medium-high speed for a couple of minutes, until the mixture becomes lighter in color.
Add in 1 egg yolk, 2 tsp almond extract, and 1 tsp vanilla extract. Mix on a medium speed until combined.
Whisk together 2 cups flour, 2/3 cup almond flour, 1 Tbsp cornstarch, and 1/4 tsp salt in a separate bowl.
Mix the flour mixture into the butter mixture on a low speed until it is JUST incorporated. Scrape the sides of the bowl with a rubber spatula between additions.
At this point, the dough should be quite thick. Divide the dough in half and wrap each portion of dough in a piece of plastic wrap. I like to flatten the dough out into a rectangle that's about 1/4 inch tall to make it easier to roll out once it's chilled.
Chill the dough in the fridge for about 45 minutes. If you need to chill the dough overnight, let it sit out at room temperature for about 10 minutes before trying to roll it out. This will make it easier to roll out!
Turn on the oven to 350°F/175°C for about 30 minutes before you plan to roll out the dough, and line two large baking sheets with silicone baking mats or parchment paper. Set aside.
Take one piece of dough out of the fridge, leaving the other in there to continue to chill. Unwrap the cookie dough and lay the plastic wrap out flat on your counter. We will be rolling out the cookie dough on the plastic wrap to make cleanup a breeze and to make it easier to cut out the cookies. Dust both sides of the cookie dough and your rolling pin with flour.
Roll the chilled dough to be 1/8 inch thick. If the dough cracks/splits a bit as you roll it out, don't worry! It will come back together as you roll it out and you can cut the cookies out around any big splits. If the dough is too soft to pick up the cut-out cookies, lift the entire sheet of cookie dough with the plastic wrap and place it in the fridge for 5-10 minutes to let it firm up.
Cut out 1 1/2-inch scalloped rounds with a flour-dusted cookie cutter. If you don't have a circle cutter that size, use a round glass that's similar in size. Then use a 3/4-inch heart cutter or circle cutter to remove the centers from half the cookies. Save the dough from the centers to be rolled out with the next piece of dough.
The cookies will spread a little bit as they bake, so place them about 2 inches apart on the prepared baking sheets.
Bake one sheet of cookies at a time. Bake for 9-10 minutes on the middle rack of your oven (bake time can vary based on the size of the cookies). Keep a close eye on the cookies and pull them out before the edges start to brown.
Let the baked cookies cool on the pan for about 15 minutes, then transfer them to a wire rack to finish cooling.
While the first batch bakes and cools, knead together the cookie dough scraps and rewrap them in plastic wrap. Pop them back in the fridge to chill.
Pull out the 2nd chilled portion of dough and repeat steps 8-12. Then repeat with the chilled dough scraps.