Preheat your oven to 300°F (150°C).

In a food processor, combine flour, icing sugar, salt, grapefruit zest, and thyme. Pulse until well-blended, about 30 seconds.

Gradually add in the cold, cubed vegan butter while pulsing. Continue processing until a rough dough ball forms (1-2 minutes).

Transfer the dough to a 9-inch fluted tart pan and press it evenly into the bottom and sides.

Bake for 35-40 minutes until edges are slightly golden.

Remove from oven and let cool for 5 minutes before cutting into 16 equal pieces.

Allow cookies to cool completely in the tart pan for optimal texture.

Sift powdered sugar into a bowl and whisk in grapefruit juice until smooth. Add coloring if desired.

Dip each cookie into the icing twice and garnish if desired before allowing to dry on a wire rack.

Let the icing dry on the cookies for about 30 minutes before serving or packaging.