Bring a pot of water to a rolling boil in on the stove and cook pasta according to package directions.
While the pasta cooks, sauté onions and garlic in oil over medium-low heat until onions are translucent.
Rinse and dry spinach in a colander or salad spinner, tear into large pieces, and add it, still damp, to the skillet with the onions and garlic. Reduce heat to low, cover pan and allow spinach to wilt (this only takes a few minutes).
When spinach is wilted, but still very bright green, use a blender to puree the sautéd spinach, onions, and garlic with the rest of the sauce ingredients (except for the Pecorino Romano and almonds) until very smooth.
Add the Pecorino Romano and blend again until combined.
In a dry skillet on medium heat, toast almonds, stirring frequently until lightly browned and aromatic (alternately: toast them on a sheet pan in a 350°F oven for 10 minutes, stirring occasionally). Remove from skillet to a small bowl.
To serve, toss hot pasta and sauce in a large bowl OR serve ladled over hot pasta.Top with more grated Pecorino Romano and lots of crunchy toasted almonds.