Cream the softened butter and sugar together in a bowl until the mixture is light, fluffy, and pale in color, about 2-3 minutes. The sound should turn from whirring to a gentle, consistent hum.
Whisk in the egg and vanilla extract until well combined, resulting in a smooth, glossy mixture that drips slowly from the spatula.
In a separate bowl, sift together the flour and matcha powder, mixing well to evenly distribute the green tea flavor and color.
Gradually add the dry ingredients to the wet mixture in parts, folding gently with a spatula until a soft dough forms. It should be slightly sticky but hold together.
Divide the dough into two equal portions. To one portion, mix in the strawberry jam until smooth and marbled throughout.
On a clean surface, gently roll or press each portion into a rectangle, then layer them slightly overlapping. Use a spatula or your hands to fold the layers together, creating a swirl or marbled effect.
Shape the combined dough into a log or flatten it into a disk, then cut into small, even pieces or slices to form individual cookies.
Place the shaped dough onto a baking sheet lined with parchment paper, spacing the cookies about 2 inches apart. Slight indentations or decorative patterns can be added now if desired.
Bake in a preheated oven at 350°F (175°C) for about 10-12 minutes, or until the edges are just golden brown and the cookies sound hollow when tapped.
Remove the cookies from the oven and let them cool on the baking sheet for a few minutes before transferring to a wire rack. They will firm up as they cool, revealing their tender crumb and marbled appearance.
Enjoy these cookies with a cup of tea or your favorite beverage, appreciating the visual swirl and tender, melt-in-your-mouth texture.
