I'll share with you this simple recipe of curry sauce.
You need:
onion
garlic
chilli powder
gram masala
cumin
curry powder
coconut milk (this will make your curry sauce tastier)
ginger
Place onions and garlic into a saucepan, add water to cover. Place over high heat and bring to a boil, reduce heat to medium-low, cover, and simmer for 45 minutes. Add the ginger, and continue simmering for 5 more minutes.
Puree the onion in a food processor or blender in batches until smooth. Place a large saucepan over medium-high heat, pour in the diced tomatoes, and season with turmeric, cumin, garam masala, curry powder, and red pepper flakes. Bring to a simmer. Simmer for 45 minutes.
Hope this helps.