Preheat the oven to 375 degrees.
Slice the heirloom tomatoes in half and lay them onto a lightly oiled baking sheet, skin sides up.
Slice the serrano peppers in half, lengthwise and lay on the baking sheet, skin sides up.
Wrap the head of garlic in aluminum foil with a splash of olive oil and dash of salt and set onto the baking sheet.
Roast 30-35 minutes until the pepper skins are nicely charred.
While tomatoes and peppers are roasting, heat a large pot to medium heat and add olive oil. Add onion and celery and cook about 5 minutes to soften.
Remove tomatoes, peppers and garlic heat and cool slightly.
Peel the tomatoes and peppers and squeeze the garlic form their skins. Add it all to the large pot.
With the heat on low, add remaining ingredients except lemon and stir.
Bring to a light boil, then reduce heat and simmer for 10 minutes, stirring occasionally.
Add lemon juice and stir.
Remove from heat.
Cool slightly and strain. A food mill works great here to remove the bulky solids.