Combine Wet Ingredients: Whisk together the milk, sour cream, melted butter, egg, oil, and vanilla in a medium bowl.
Mix Dry Ingredients: In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
Combine Wet and Dry Ingredients: Use a large rubber spatula to scrape the milk mixture into the dry ingredients and use a gentle folding motion to mix the two until 80% incorporated (there will still be floury streaks).
Add Rhubarb and chocolate: Add the chopped rhubarb and chocolate and continue folding to just combine.
Prepare Baking Sheets: Drop batter by 1 1/2 tablespoonfuls 2" apart onto parchment-lined baking sheets. Sprinkle with a bit of coarse sugar.
Bake: Bake for about 11 minutes, until tops are bouncy when pressed and the tops are lightly golden. You don't want an underbaked middle for these cookies.
Cool: Transfer immediately to wire racks to cool.
Video
Notes
For perfect cookies: Take the cookies out at 9 minutes before the dough is fully set and use an overturned glass to gently re-shape them into perfect circles. Top with a few extra chocolate chips then continue baking about 3 minutes more.Room Temperature Ingredients: Ensure milk, sour cream, butter, and eggs are at room temperature for a smooth mixture and better-textured cookies.Finely Chop Rhubarb: Create even distribution and prevent big, raw chunks by finely chopping the rhubarb.Use a Rubber Spatula: Gently fold wet and dry ingredients with a rubber spatula to avoid overmixing and preserve fluffiness.Parchment Paper is Your Friend: Use parchment paper for easy clean-up, protection from direct heat, and effortless cookie removal.Full Bake is the Way: Fully bake for optimal texture and flavor—look for bouncy tops and no more shine.Frozen Rhubarb Works Too: Thaw and drain frozen rhubarb thoroughly before chopping and adding to the batter. It's a great alternative if fresh rhubarb is unavailable.