Dice the onion and chop the tomatoes, dice the garlic as well. Melt the butter in a sauce pan and add onion when butter has completely melted. Stir and sweat the onion for about 5 minutes. Add garlic and stir about 1 minute or 2, you don't want to burn the garlic. Add chopped tomatoes and stir occasionally for about 8-10 minutes. Add remaining ingredients and combine thoroughly. Reduce heat to a simmer and let the flavors combine for about 1/2 hour. Remove from heat and let cool enough to puree in a blender. Puree and then return to cleaned sauce pan or bowl; it's now ready for use.