slightly adapted from Saveur and More Than Burnt Toast
Streusel:
½ cup flour
½ cup sugar
2 tablespoons packed light brown sugar
½ teaspoon lemon zest
½ teaspoon kosher salt
¼ teaspoon almond extract
4 tablespoon unsalted butter, grated
½ cup chopped almonds
Muffins:
Unsalted butter, for greasing
3 cups flour, plus more for pan
2 teaspoons baking powder
½ teaspoon kosher salt
¼ teaspoon baking soda
1 cup sour cream
1 cup sugar
½ cup packed light brown sugar
½ cup canola oil
2 eggs, lightly beaten
1 vanilla bean, seeds scraped and reserved
½ teaspoon almond extract
12 oz. rhubarb (about 2 medium stalks), cut into quarter inch pieces
Make the streusel: Whisk together flour, both sugars, zest, salt, and extract in a small bowl. Grate butter into mixture using large box grater. With your fingers, rub into almond mixture until smooth and large clumps form. Stir in almonds and transfer to refrigerator; chill until ready to use.
Make the muffins: Heat oven to 350°. Grease and flour muffin pans or use muffin liners; set aside. Whisk together 2 ¾ cups flour, baking powder, salt, and baking soda in a large bowl; set aside. In another bowl, whisk together sour cream, both sugars, oil, eggs, almond extract and vanilla seeds; pour mixture over dry ingredients and whisk until just combined.
In a small bowl, toss remaining flour with rhubarb until evenly coated, and then stir into batter. Working in batches, place cup batter in muffin cups, break streusel up into medium-sized clumps, and sprinkle evenly over muffins. Bake until golden brown and a toothpick inserted in the middle of each muffin comes out clean, about 30 minutes. Let cool 10 minutes before serving.