Preheat your oven to 350°F (180°C) and line a baking sheet with parchment paper.
In a mixing bowl, beat the softened butter and sugar together with an electric mixer until the mixture is light, fluffy, and pale in color, about 2-3 minutes. The sound should be a consistent creaming noise.
Add the egg to the butter mixture and beat until fully incorporated, ensuring a smooth and slightly glossy texture.
In a separate bowl, sift together the flour and matcha powder to evenly distribute the green tea flavor and color, which will give the dough a vibrant shade.
Gradually add the dry ingredients to the wet mixture, mixing on low speed until a soft dough forms. The dough may be slightly crumbly but should hold together when pressed.
Divide the dough into two equal parts. Place one part on a lightly floured surface and gently roll it into a flat rectangle about 1/2 inch thick.
Spread half of the strawberry jam evenly over the rolled dough, leaving a small border around the edges to prevent overflow during swirling.
Carefully roll the dough into a tight log from the short end, then gently press to seal the edge. Repeat with the second half of dough and remaining jam.
Use a sharp knife to slice each log into about 1/2-inch thick cookies. Place the slices on the prepared baking sheet, spaced slightly apart to allow for spreading.
Bake the cookies in the preheated oven for 10-12 minutes, or until the edges are lightly golden and the marbled swirls become beautifully defined.
Remove the cookies from the oven and let them cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely. The cookies should be tender with a slight crisp at the edges, showcasing the swirl pattern.
Enjoy these colorful, fragrant cookies with a cup of tea or milk, marveling at their marbled appearance and contrasting flavors.
