Cut rhubarb into small, uniform pieces and toss with a tablespoon of flour before folding into batter to prevent them from sinking and to help distribute moisture evenly throughout the cake.

Use a microplane zester to extract only the bright outer layer of the orange peel, avoiding the bitter white pith, and add it directly to the dry ingredients to infuse maximum citrus flavor.

Bring buttermilk to room temperature before adding to ensure proper emulsification with other ingredients, resulting in a tender, evenly-textured crumb rather than a dense cake.

Beat softened butter with coconut sugar for 3-4 minutes until pale and fluffy to incorporate air, which creates lift and prevents a heavy, compact cake texture.

Fold in the rhubarb gently at the very end and mix the final batter only until just combined to avoid developing gluten, which toughens the cake and makes it less moist.