Preheat oven to 350°F / 177°C. Line a muffin tin with paper liners and spray it lightly with nonstick spray.
Start by making the streusel topping. In a small bowl, stir together 1/3 cup flour, 3 Tablespoons brown sugar, granulated sugar, and a pinch of salt. Pour the melted butter over top and use a fork to mash everything together until even. Refrigerate the streusel until you’re ready to use it.
In a large mixing bowl whisk together the eggs, 1 cup light brown sugar, and oil until smooth and frothy. Sprinkle the cinnamon, baking soda, and baking powder over the top and then whisk well until no dry spots remain. Add 1 1/2 cups of flour and stir gently just until the flour is evenly incorporated (don’t over mix).
Gently mix in the carrots, walnuts, and raisins.
Fill the muffin tin with batter, about 2/3 of the way to the top. Remove the streusel from the refrigerator and crumble it over the muffins.
Bake until a tester inserted in the center comes out clean, 20 to 22 minutes.
While the muffins bake, use a hand mixer or standing mixer to beat the cream cheese until very smooth. Add the sugar, milk, and vanilla. Beat everything together, starting on low and increasing the speed, until the glaze is very smooth and glossy.
When the muffins are done baking, let them cool for about 5 minutes and then drizzle with glaze. If not serving right away, wait to add the glaze until right before serving.