For Sable Cookies

1. Line baking sheet with parchment paper or a nonstick baking mat; set aside.
2. Place butter and sugar in the bowl of a food processor; process until creamy. Add egg yolks, salt, and vanilla; process for 30 seconds until combined. Add 1 cup flour and process until smooth. Add remaining cup of flour to processor; process to combine. Turn dough out onto work surface and split in half, forming each half into a flat disc; wrap with plastic wrap and transfer to refrigerator until chilled.
3. Flour your work surface and roll out half of the dough until it is 1/8-inch-thick. Using a small fluted heart shaped cookie cutter, cut out dough and transfer to lined baking sheet. Gather scraps and place in fridge with the baking sheet to chill.
4. Repeat using the second half of dough.
5. Roll out scraps and repeat. All of your cut out cookies should chill for 30 minutes before baking – this will keep the cookies spreading in the oven.
6. Preheat oven to 325 degrees.
7. Mix together remaining egg yolk with 1 teaspoon water; brush tops of cookies with egg yolk mixture. Transfer to oven. Bake until cookies are pale golden, 12 to 15 minutes. Transfer to a wire rack to cool.

For Ombre White Chocolate Topping

1. Once the cookies are cool, separate the white chocolate between 4 microwave safe dishes. Melt according to package directions, one at a time.
2. Add in desired food coloring. I used increasing amounts of red dye to achieve shades of pink and one red with one drop blue dye for purple. (Note: White chocolate will seize if it is over worked. I found that as I added more food coloring, it significantly thickened.)
3. Frost your cookies.