Cream butter and sugar until smooth and fluffy (2–3 minutes).
Add egg, egg yolk, vanilla, and almond extract; mix until combined.
Whisk flour, cornstarch, baking powder, and salt separately.
Gradually mix dry ingredients into wet ingredients until just combined.
Chill dough for at least 1 hour.
Divide dough into four portions.
Color three portions with gel food coloring (leave one white).
Roll colored doughs to ⅛-inch thickness.
Cut small to medium hearts from colored dough; set aside.
Roll white dough to ¼-inch thickness.
Arrange colored hearts on top of white dough.
Place parchment over dough and gently roll to secure hearts.
Cut large heart shapes from layered dough.
Chill cut cookies 10–15 minutes.
Bake at 350°F for 8–9 minutes.
Remove when centers look slightly underdone and edges are not browned.
Cool on baking sheet 5 minutes, then transfer to rack.
Gather leftover dough scraps and gently fold to create a marbled effect.
Roll to ¼-inch thickness, cut additional hearts, and bake as directed.