Recipe Garam masala

[BWF]

I've been trying to make my own Garam masala for a while how without much success. I wonder if anyone here has any tips on making the perfect garam masala?

I usually use the following ingredients in a variety of combinations, but the problem I have is the roasting of the spices. What happens is that the timing must be just right as some spices cook faster than others and I usually end up with some spices over-cooked and others under-cooked.

Ingredients:

• 4 tbsps coriander seeds
• 1 tbsp cumin seeds
• 1 tbsp black peppercorns
• 1 ½ tsps black cumin seeds
  
• 1 ½ tsps ginger powder
  
• 3-4 large black cardamoms
  
• ¾ tsp cloves
• 2 cinnnamon sticks
  
• 2 bay leaves

I simply roast everything in a skillet over a low to medium flame. When the spices turn brown, I leave them to cool and then grind them to a fine powder with my coffee grinder.

I wonder if anyone has any tips for a better recipe or method?