In a large pot, melt 1 tablespoon of butter over medium heat. Add diced onion and minced garlic, stirring occasionally for about 4-5 minutes until the onion becomes translucent and fragrant.

Next, toss in the chopped Yukon Gold or Russet potatoes, stirring well to coat them in the buttery mixture. Cook for 5-7 minutes, allowing the potatoes to start softening but not browning.

Pour in 4 cups of seafood stock, raising the heat to bring the mixture to a gentle simmer. Allow it to cook for 10-12 minutes, during which the potatoes should become fork-tender.

Reduce the heat back to low, then stir in 1 cup of heavy cream and 1 cup of whole milk into the pot. Gently heat this mixture for 2-3 minutes until it’s smooth and velvety.

Add in the white fish, shrimp, scallops, and mussels, ensuring they are evenly distributed throughout the chowder. Cook for another 5-7 minutes until the seafood is opaque.

Finally, stir in fresh thyme and bay leaf, seasoning with salt and pepper to taste. Allow the chowder to heat through for an additional 2-3 minutes before serving.