Add all the ingredients for the vanilla cookie dough to a large mixing bowl and stir together with a fork or electric mixer. Mix until the dough comes together into a ball (if mixing by hand, use your hands to knead the dough). Don't overwork the dough.
Wrap the dough in plastic wrap and chill in the refrigerator for about 20 minutes. Repeat for the chocolate cookie dough.
Roll out just over half of the vanilla dough so that it is about 1 cm (1/2 in)) thick evenly all over, about 10×15 cm (4x6 in). Then cut 8 1 cm wide sticks from the dough. They will be about 15 cm (6 in) long.
Do the same with just over half of the chocolate dough. Put the sticks of dough in the fridge for 10 minutes. Then build the checkerboard by placing every other vanilla and chocolate in 4 rows wide and 4 rows high. Make sure they are completely pressed together. You do this by pressing gently and constantly shaping into a square.
Roll the rest of the light and dark dough into thick sausages and divide them in half lengthwise. The sausage needs to be the same thickness as the square checkerboard log you built above. Place the vanilla on one side of the checkerboard log and the chocolate on the other. Press and shape it so that it has the shape of a heart.
Preheat oven to 350°F (175°C) and line a baking sheet with baking paper.
Slice into cookies, about 7 mm (1/4 in) thick and place on your baking sheet.
You can use the remaining vanilla and chocolate dough to make another checkerboard (without the heart addition) or simply roll the dough into logs and slice plain chocolate and vanilla cookies from them.
Bake for about 12 minutes, until the vanilla dough just starts to turn golden.