Preheat oven to 350F.

Saute the rhubarb in butter until tender, then cool.

Cut a strip of parchment to fit the loaf pan with enough for some to hang over the sides.

Spray the bottom of the pan lightly with nonstick cooking spray to get the parchment to stay in place, then spray the parchment with additional spray.

Place the flour in a mixing bowl and add the berries, tossing them to coat, then lift them out, shaking off the excess flour and holding the floured berries in a small bowl.

Add the baking powder, baking soda, salt and cinnamon to the flour and mix well.

Whisk the eggs with the sugar, milk, and vanilla, and stir in the butter and rhubarb.

Add the flour mixture and stir to form a batter then fold in the blueberries.

Spread the batter in the loaf pan and top with the crystal sugars.

Bake in the preheated oven for 60-65 minutes or until a toothpick can be inserted and removed without wet batter clinging to it.

Cool in the pan 15 minutes, then lift out using the parchment tabs and finish cooling on a wire rack.

Remove the parchment and slice with a serrated knife, storing unused portions in an airtight container.