Wow!!! Thank you sooooooo much for the advice!
I really needed some scientific baking explanations.
I use 1 tsp of baking powder in 4 cups of flour.
When I baked Lindy Smith's Vanilla Cookie Recipe, I had no bubbles whatsoever, but I found the cookie very dense. The cookie dough was made by rubbing diced butter into the flour (+ baking powder) and sugar then adding wet ingredients including eggs and golden syrup. It tasted divine but it was a tough cookie. I propose to try adding more golden syrup since it contains invert syrup which is made up of glucose and fructose. The glucose should keep the cookie chewy on the inside and crisp on the outside.
Do you perhaps know the science behind the flour to butter ratio, eg. the more flour to butter might mean the cookie would be more tougher.