Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large bowl, cream together the softened butter and sugar until fluffy. Then, incorporate the eggs and vanilla extract, mixing well until everything is combined.

In another bowl, whisk together the all-purpose flour, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, mixing just until combined.

Split the dough into three equal portions in separate bowls. In one portion, mix in the cocoa powder for chocolate flavor. In the second portion, add the strawberry jam or puree. The third portion can remain plain or be tinted with food coloring.

Take small amounts of each colored dough and place them side by side or on top of each other on the prepared baking sheet. Gently swirl with a knife or toothpick.

Bake the cookies for 10 to 12 minutes or until the edges are lightly golden. Let them cool on the baking sheet for a few minutes before transferring to a wire rack.