In a medium bowl, combine flour, corn starch, baking powder, and salt. Stir to combine.
Add in the cold butter in 4 – 5 chunks. Use a fork to blend the butter into the flour until the mixture looks crumbly and the butter is evenly distributed in small lumps throughout the flour mixture. This should take a few minutes to make sure there are no large clumps remaining.
In a separate small bowl, mix the yogurt, cream, milk, and egg. Stir to combine.
Stir the wet mixture into the flour mixture until dough ball forms and gathers along the side of the bowl. If it’s a little wet and doesn’t hold a ball shape you can add about a tablespoon of flour and stir to see if it holds together better. If the mixture is too dry and doesn’t come together, you can add a teaspoon of milk and stir again.