Preheat oven to 375ºF. Line a muffin tin with paper liners.
Make the streusel. In a small bowl, combine pistachios, flour, and brown sugar. Using a fork, cut the butter cubes into the pistachio mixture until it resembles coarse crumbs. Set the bowl aside.
For the muffins, start by combining dry ingredients (flour, baking powder, baking soda, and salt) in a medium bowl.
In a large bowl, whisk ricotta, sugar, eggs, vanilla, orange zest, orange juice, oil, and rosemary until smooth.
Gently fold the dry ingredients into the wet ingredients. Do not overmix.
Scoop batter into prepared muffin pan, filling cups about 3/4 of the way. Top with the pistachio streusel, adding generously on top.
Bake 20-25 minutes until a toothpick comes out clean. Let muffins cool in the pan 5 minutes, then transfer to a wire rack to cool.
Once the muffins are cool, drizzle with the orange glaze. To make the orange glaze, whisk the powdered sugar with orange juice and pinch of salt. The consistency should be thick enough to drizzle.