Heat oven to 375 degrees.
Place cold butter in a microwave safe bowl, and heat for 30 seconds or until it starts to soften. Add the margarine and heat again another 15 seconds until both are just starting to melt, but not melted.
In a large bowl, stir the softened butter/margarine, sugars, and egg until mixed.
Pour in the flour, baking soda and salt. Stir. (dough will be stiff.)
Stir in chocolate chips.
Drop dough by rounded Tablespoonfuls, about two inches a part onto ungreased cookie sheet or baking mat. Bake 8 to 10 minutes or until light brown. (centers will be soft).
Cool for 15 minutes. Remove from cookie sheet and cool on wire rack.