Prep the oven: Arrange a rack in the middle of the oven and preheat to 425℉/218℃.
Defrost the spinach: Remove the packaging and place 10 ounces frozen chopped spinach in a medium bowl. Microwave according to package instructions until fully defrosted. Using your hands or a cheesecloth, squeeze out as much liquid as possible from the spinach.
Saute the aromatics: In a medium skillet or saute pan, add 1 tablespoon extra-virgin olive oil and set over medium heat. Saute 1 jalapeno pepper, 1 clove garlic, 1 large shallot, and ½ teaspoon red pepper flakes (if using) for 5 minutes until softened and lightly golden-brown. Add the spinach (reserving the medium bowl for later) and 1 (14-ounce) can marinated artichoke hearts, and saute for 5 minutes until moist of the moisture has evaporated. I like to break up the artichokes with a wooden spoon so there aren't any large pieces.
Mix the dip: In a medium bowl, add 8 ounces full-fat cream cheese, and use a spatula or large spoon to break up the cream cheese into a homogeneous paste. Add ½ cup full-fat sour cream, 6 ounces pepper jack cheese, ½ cup freshly grated parmigiano-reggiano cheese, 1 tablespoon balsamic vinegar, and ¼ cup pickled jalapeno peppers. Taste and season the dip with salt, as desired. Note: The dip should be well-balanced and seasoned for the best flavor, so make sure to add more salt if needed! It should taste salty, spicy, and tangy. Want it spicier? Add some more red pepper flakes. Want it tangier? Add a bit more balsamic.
Combine and bake: Stir the artichoke-spinach mixture into the bowl and toss to combine. Transfer to a casserole and spread in an even layer. Bake for 20 - 25 minutes until lightly golden brown on top.Let cool for about 5 minutes before serving.
Notes
TIP: I prefer a chunkier dip, but if you want a more homogeneous texture, you can finely chop the spinach and the artichoke hearts before sauteeing.Serving Suggestions: Serve with tortila chips, pita chips, crostini, or fresh crudites.Leftover dip can be stored in an airtight container in the fridge for 3 - 4 days.