1. Preheat your oven to 410°F. Line baking sheets with parchment paper.
2. In a large bowl, cream the cold cubed butter with both sugars until just combined. You’re not looking for fluffy here, just mixed.
3. Add the cold eggs and vanilla. Mix until incorporated, scraping down the bowl as needed.
4. In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt.
5. Add the dry ingredients to the wet mixture and mix just until a thick dough forms.
6. Fold in the white chocolate chips, milk chocolate chips, and Valentine confetti until evenly distributed.
7. Portion dough into large bakery-style balls. They should resemble large loose sptheres. Place no more than 4 cookies per pan, spacing them well apart.
8. Bake for 8–10 minutes. The tops should look just set, but the centers will still be soft.
9. Remove from the oven and do not move the cookies. Let them cool on the pan for at least 30 minutes.
10. Carefully transfer to a cooling rack and let them finish setting for 2–3 hours before serving.

These firm up beautifully as they cool and get that classic thick Levain texture with a soft middle and structured edge.