Preheat oven to 350°F (175°C) and line two large baking sheets with parchment paper.

In a medium bowl, whisk together 3 cups flour, baking soda, baking powder, and salt.

In a large bowl, cream the softened butter, 1 cup granulated sugar, and brown sugar until light and fluffy (3-4 minutes).

Mix in the eggs one at a time, followed by the vanilla extract.

Gradually mix in the dry ingredients on low speed until just combined. Do not overmix.

Divide the dough equally into two bowls.

To the first bowl, fold in the sweetened condensed milk and 2 tablespoons of extra flour until smooth.

In a small dish, mix hot water, espresso powder, and cocoa powder into a paste. Fold this paste into the second bowl of dough until completely dark brown.

Cover both bowls and chill in the refrigerator for at least 30 minutes.

Take 1 tablespoon of milk dough and 1 tablespoon of espresso dough, press them together, and gently roll into a ball to create a marbled effect.

Roll the marbled dough balls in the remaining 1/3 cup of granulated sugar and place on baking sheets 2 inches apart.

Bake for 11-13 minutes until edges are set but centers are still soft. Cool on the pan for 5 minutes before moving to a wire rack.