1) To make the chocolate cookies: Melt the chocolate with the butter, in a microwave oven or double boiler set over a burner. Set it aside.
2) In a large bowl, mix together the sugars. Pour the chocolate/butter into the bowl, stirring to combine.
3) Add the corn syrup, vanilla, egg, espresso powder, baking powder, baking soda, salt, and cocoa, stirring to combine.
4) Stir in the flour; the dough will be soft and smooth. Cover it, and refrigerate for 1 to 2 hours, until it's solidified and stiffened up.
5) While the chocolate dough is chilling, make the vanilla cookie dough.
6) Lightly grease (or line with parchment) a couple of baking sheets. Preheat the oven to 375°F.
7) Using a very slightly heaped tablespoon cookie scoop, drop six balls of vanilla cookie dough on one of the baking sheets, then six balls of chocolate cookie dough, spacing them evenly with about 2" between them. If you don't have a tablespoon cookie scoop, the dough balls should be a generous 1 1/4" in diameter. Gently flatten each ball of dough to about 2" across.
8) Bake the cookies for 10 minutes. While they're baking, prepare your next sheet of cookies for the oven.
9) Remove the cookies from the oven, and set your timer for 4 minutes. After 4 minutes, use a 1 3/4" to 2" heart-shaped cutter to cut a heart out of the center of each of the cookies. Quickly transfer the hearts to cookies of the opposite flavor, gently pressing them into the heart-shaped opening in the center of each. You'll now have vanilla cookies with chocolate hearts, and chocolate cookies with vanilla hearts.
10) Change the look by putting the vanilla hearts bottom-side-up in the chocolate cookies; the bottom of the cookie will be medium-gold, rather than cream-colored. This yields more of a "heart of gold" look.
11) Repeat with the remaining cookie dough. You'll have some leftover vanilla cookie dough, enough to make about 8 cookies. Cut hearts out of the center, and flip them over so the bottom's on the top: heart of gold!
Yield: about 4 to 4 1/2 dozen cookies.