Step 1
Whisk 3 Tbsp. gochujang (Korean hot pepper paste), 2 Tbsp. soy sauce, 1 Tbsp. chicken or vegetable bouillon paste, 1 Tbsp. sugar, 2 tsp. fish sauce, and 1 cup water in a medium high-sided skillet to combine.
Step 2
Slice one 14-oz. block firm tofu, drained, in half lengthwise, then cut crosswise into 6 sections to create 12 squares. Arrange in pan in a single layer (you can shingle slightly if needed). Scatter 1 small white or yellow onion, cut into ½”-thick wedges, 4 garlic cloves, coarsely chopped, and 1 Tbsp. unsalted butter, cut into pieces, on top. Set pan over high heat and bring to a boil. Cook, spooning sauce over tofu occasionally, until sauce is reduced by about a third, 5–7 minutes.
Step 3
Remove pan from heat. Add 1 tsp. toasted sesame oil and remaining 3 Tbsp. unsalted butter, cut into pieces, and stir gently and swirl pan until butter is melted and incorporated into sauce.
Step 4
Crush seasoned toasted seaweed snacks into large shards and scatter over tofu. Serve with cooked rice alongside.