Preheat oven to 400 degrees Fahrenheit. Line a baking sheet with parchment paper or a silicone baking mat.
In a large bowl, whisk together flour, sugar, brown sugar, baking powder, baking soda, salt, cinnamon, and nutmeg. Cut in butter until the mixture resembles coarse crumbs. Stir in fresh rhubarb.
In a small bowl, whisk together milk, egg, and vanilla extract.
Add wet ingredients to dry ingredients, and stir until just combined.
Turn the dough out onto a well-floured surface. Gently knead 5-6 times or until the dough just comes together.
Gently shape dough into an approximate 7-8 inch circle. Cut into 8 pieces, and place on the prepared baking sheet. Sprinkle with coarse sugar, if desired.
Bake for 20-25 minutes, or until edges start to turn light golden brown. Remove to a wire rack to cool.
Store leftovers in an airtight container.