Preheat oven to 400 degrees F (200 degrees C). Line a 12-cup muffin tin with paper liners.
In a large bowl, whisk together flour, sugar, baking powder, and salt.
In a separate bowl, whisk together milk, oil, and eggs. Add wet ingredients to dry ingredients and stir until just combined. Do not overmix.
In a small bowl, combine flour, brown sugar, butter, and cinnamon for the streusel topping. Use a pastry blender or your fingers to cut the butter into the mixture until it resembles coarse crumbs.
Fill muffin liners about 2/3 full. Sprinkle streusel topping evenly over muffins.
Bake for 18-20 minutes, or until a wooden skewer inserted into the center comes out clean.
Let cool in the muffin tin for a few minutes before transferring to a wire rack to cool completely.