Toss chopped rhubarb with 2 tablespoons sugar and let sit for 30 minutes, then drain excess liquid.
Preheat oven to 200°C (392°F) and line a baking tray with parchment paper.
Mix flour, baking powder, baking soda, salt, and sugar in a bowl.
Cut in cold butter until mixture forms uneven crumbs with some pea-sized pieces.
In a separate bowl, mix sour cream, milk, and vanilla.
Combine wet and dry ingredients gently until a shaggy dough forms.
Fold in rhubarb and optional ginger without overmixing.
Turn dough onto a lightly floured surface and shape into a round about 2–3 cm thick.
Cut into wedges and place on prepared baking tray.
Chill or freeze for 15 minutes before baking.
Bake for 15–22 minutes until edges are golden and bottoms are lightly crisp.
Cool for 10 minutes before serving.