In a saucepan, cook the butter and sugar on low for about 5 minutes, until the butter is melted and the sugar has completely dissolved, stirring continuously. Add the vanilla and lemon zest and set aside to cool slightly.

In a separate bowl, mix the flour, ground almonds, baking powder, baking soda and salt until well combined. Pour the butter and sugar mixture into the flour mix and stir with a wooden spoon.

Measure the dough and divide it in half. Place each half in a separate bowl and add the matcha powder to one and the black sesame butter to the other. Mix gently, until well combined. Refrigerate both bowls for at least 20 minutes.

Preheat the oven to 375°F (180°C), and line two baking sheets with parchment paper or silicone mats. Position the racks to divide the oven into thirds.

Take the dough out of the fridge. Scoop out about 2 teaspoons (10 g) of dough from each bowl, combine them gently in your hands and roll into a ball. Do not over-roll, roll just enough to form a ball. Each ball should be approximately 1 ounce (25 to 27 g). Place the balls on the prepared baking sheet, about 2 inches (5 cm) apart (they will spread).

Bake for 10 to 12 minutes, until flattened and set on the edges. They should remain slightly soft in the center. Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.

These cookies will keep well for up to 3 to 4 days, in an airtight container, at room temperature. You can also freeze them for up to 2 months.