Place large, cast-iron skillet on stovetop over medium-high heat. When skillet is hot, add 4 ounces dried guajillo chiles to skillet, arranging chiles in single layer without stacking or overlapping.. Work in multiple batches if needed.
Toast chiles 15 to 20 seconds or until fragrant and slightly puffy. Transfer toasted chiles to cutting board and set aside to cool. Repeat process with any remaining dried chiles.
Once all chiles have been toasted and cooled, cut off and discard stems of chiles. Slice chiles into strips.
Place guajillo strips and seeds in medium saucepan. Add 2 cups hot water and place saucepan on stovetop over high heat.
Bring water to rolling boil. Boil chiles 5 minutes.
After 5 minutes, add 1 whole roma tomato to saucepan. Boil tomato 30 seconds, then immediately transfer chiles, tomato, and 50% of seeds to food processor bowl using slotted spoon. Set saucepan of water aside.
Place large, cast-iron skillet on stovetop over medium-high heat. When skillet is hot, add 4 large cloves fresh garlic to pan.
Toast garlic, flipping cloves frequently, approximately 8 minutes or until cloves are tender and skins are lightly charred.
Transfer charred cloves to cutting board and set aside. Once cloves have cooled, peel cloves and discard skins. Trim and discard ends of cloves.
Transfer toasted garlic to food processor bowl with guajillo chiles and boiled tomato. Add 1 ½ teaspoons kosher salt, 1 tablespoon white vinegar, 1 teaspoon garlic powder, 1 teaspoon onion powder, 1 whole roma tomato, and 2 large cloves fresh garlic.
Pulse ingredients in food processor until puréed into thick paste.
Add reserved water to food processor in small increments, pulsing mixture to fully incorporate water after each addition. Repeat until desired consistency is achieved.
Once salsa is thinned as desired, taste salsa and add additional garlic and/or salt if desired. Pulse mixture to fully incorporate any added ingredients.
When satisfied with flavor of salsa, transfer prepared salsa to serving bowl and serve as desired.