1. Preheat oven to 350F/180C. Line baking sheets with baking paper. In a large bowl mix together the dry ingredients [flour, salt, baking soda & cornstarch if using] and set aside.
2. In the bowl of an electric mixer, cream together the margarine, coconut oil and sugar. Mix for about 2 minutes.
3. Add the eggs and vanilla. Mix until just blended.
4. Add the flour mixture and mix until combined. Then add in the chocolate chips.
5. Using a medium ice cream scooper, spoon dollops of dough onto the baking sheet. Leave plenty of space between as these cookies spread. I found the best size for these cookies were a dollop of 40-50g.
6. Bake for 10-12 mins. Smaller cookies will be crispier and larger cookies will be chewier. Cool for 5 mins and then transfer to a cooling rack for extra crisp. Cookies will freeze well in an airtight container.