Bring a large pot of salted water to a boil and cook the linguine according to package directions until al dente.
While the pasta cooks, pat the shrimp dry with paper towels and season lightly with sea salt and black pepper.
In a large skillet over medium heat, melt the grass-fed butter with the olive oil until shimmering.
Add the minced garlic and red pepper flakes to the skillet, sautéing for about 1 minute until highly aromatic but not browned.
Increase the heat to medium-high and add the shrimp in a single layer, cooking for 2 minutes per side until pink and opaque.
Stir in the lemon juice, lemon zest, and baby spinach, allowing the spinach to wilt slightly in the residual heat.
Reserve 2 tablespoons of the pasta cooking water, then drain the linguine.
Add the linguine and reserved pasta water to the skillet, tossing everything together to coat the noodles in the garlic butter sauce.
Garnish with fresh chopped parsley and serve immediately while hot.