• Drain peppers from liquid and reserve on paper towels.

To make a bechamel sauce for the filling, start with creating the roux:

• For the roux, melt 3 Tbsp butter and add the flour and stir on medium heat with a rubber spatula to ensure the roux cooks evenly.
• Take roux off the heat after about ten minutes, or when the flour is cooked and the roux is a pale yellow color.
• In a separate bowl, warm the milk until it is just below simmering.
• Slowly whisk in the hot milk into the hot roux, cooking over low heat.
• Make sure to add a small amount of milk at a time, combining thoroughly to avoid any lumps.
• When you have added all the milk and achieved the desired thick consistency, taste the bechamel and adjust seasoning with salt.
• You want the bechamel mixture to be very thick at this stage. Turn off heat and cover the bechamel with plastic wrap.
• In a medium saute pan with 2 Tbsp melted butter, cook the onion over medium heat for 10-12 minutes.
• Add the tomato puree or tomate frito and cook for an additional 30 minutes.
• Add the garlic clove and cook for an additional 10 minutes.
• Blend the onion and tomato mixture with 1 jar of the preserved piquillo peppers and add in the olive oil.
• Blend until smooth and fully emulsified.
• Take half of this tomato pepper sauce and whisk it fully into the warm bechamel filling.
• Take the two ounces of grated Manchego cheese and fold this cheese into the mixture.
• After you add the cheese, taste the mixture for seasoning levels. Adjust with salt & pepper if necessary.
• Cool this filling mixture down at room temperature.
• Peel and clean the shrimp.
• Salt shrimp and blanch in boiling salted water for 2-3 minutes, and then remove from hot water and cut into ¼” pieces.
• Mix the par-cooked shrimp with the tomato-pepper bechamel sauce and adjust seasoning level if needed.
• Using a small spoon, carefully spoon the shrimp filling into the remaining drained piquillo peppers, pressing down the filling with the spoon to fully stuff the peppers.
• Pour the remaining tomato-pepper sauce on the bottom of a casserole dish.
• Carefully place the whole peppers stuffed with shrimp mornay filling on top of the tomato-pepper sauce.
• Bake in a 300F oven for 45 minutes, or until the dish is fully hot throughout and the shrimp are cooked through.
• Serve hot, with extra sauce from the casserole dish poured on top of the stuffed peppers.