Bake for 15-20 minutes until the dip bubbles at the edges and the panko is golden brown.Stir the remaining 2 tablespoons panko and 1 tablespoon Parmesan together in a small bowl, then sprinkle evenly over the surface of the dip.Spread the dip in a wide gratin dish–use one that’s going to give you a shallow but wide surface for the dip, so it’s not layered too deeply.Save the remaining clam juice for use in pasta or chowder. I like it when it’s longer a thick paste, but is more scoopable and spreadable. The panko will absorb most of the liquid in the pan, so stir in 1/4 to 1/2 cup of the reserved clam juice until the dip loosens to your preferred consistency.Cook until the liquid in the skillet comes to a simmer, then whisk in the flour, lemon zest, 1/2 cup panko, and 1 teaspoon Parmesan.Add the whole can of clams (with juice) and the clams (but not the juice) from the other 2 cans.Cook for 1-2 minutes more to soften the garlic. Add 1 more tablespoon butter with the garlic, red pepper flakes, parsley, and oregano.Keep an eye on them to make sure they don’t start to brown too much.

Cook for 5-7 minutes, stirring frequently, until the onions are very soft. Melt 3 tablespoons butter in a large skillet over medium-low heat, then stir in the shallot or onion.Strain 2 of the cans of clams, reserving the clams and juice in separate bowls.