In a large mixing bowl, combine first five ingredients and mix until smooth. Add flour, baking soda, and salt; beat until soft dough forms. Remove half of dough and place in plastic bag or container; set aside.

In a small bowl, combine jello powder and boiling water. Add to remaining dough in bowl and mix until fully incorporated.

On a large piece of waxed or Gefen Parchment Paper, roll out strawberry dough into a rectangle about quarter-inch (.6-cm) thick. On a separate piece of paper, roll out vanilla dough; invert over strawberry dough and even out the edges until they’re aligned. (It doesn’t have to be perfect, the end cookies will still taste good!)

Starting at one end of length of rectangle, begin rolling up the dough, jelly-roll style, removing paper as you go along. Wrap roll in plastic wrap and chill in refrigerator until firm. Meanwhile, preheat oven to 375°F (190°C). 

Remove roll of dough from refrigerator, discard wrap and slice into eighth-inch (.3-cm) slices. Place on parchment-lined baking sheets and bake for 10–12 minutes, or until lightly browned. Remove from oven and allow to cool.