Cream the Butter and Sugar: Beat the softened butter and sugar together until the mixture is pale and fluffy, about 2 minutes. This step builds the air into the dough that keeps the shortbread tender instead of dense.

Add the Egg Yolk and Extracts: Mix in the egg yolk, vanilla, and almond extract until fully combined. The dough will look slightly glossy at this point, which is normal.

Mix in the Flour and Salt: Add the flour and salt and mix on low speed just until the dough comes together. Stop as soon as you no longer see dry flour. Overmixing here is what makes shortbread turn tough instead of tender.

Chill the Dough: Cover the dough and chill it in the fridge for about 20 minutes. This firms up the butter so the hearts hold their shape instead of spreading flat in the oven.

Shape the Hearts: Roll the dough into 1-inch balls and place them on a parchment-lined baking sheet, a couple inches apart. Using your thumb, press a V shape into the top of each ball, angling your thumb in from two sides to meet at a point in the middle. Pinch the bottom point of the V a little as you go.

Chill Again Before Baking: Pop the shaped cookies back in the fridge for 15 to 20 minutes before baking. Baking from a chilled state keeps the heart shape crisp instead of letting it soften and round out.

Bake: Bake at 350°F for 15 to 17 minutes, until the edges are just barely golden. The centers will still look pale and the heart shape will look open and defined.

Cool Completely: Let the cookies cool completely on the baking sheet or a wire rack before filling. The heart shape actually opens up more as the cookie bakes and sets while cooling, so if you try to fill it warm, the jam will just slide off.

Fill with Jam: Once the cookies are fully cool, spoon a small amount of the strained jam into the heart center of each one. Fill just to the top of the well, not over it, so the heart shape stays visible.