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1
Whisk the flour, sugar, cardamom, and salt in a medium bowl until combined.
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2
Add the butter and combine with your fingers, rubbing the butter into the flour until mostly incorporated but some small pieces remain.
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3
(The streusel is ready when it holds together in large clumps when squeezedit will still be fairly dry.)
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4
Refrigerate until ready to use.
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5
Heat the oven to 375 degrees F and arrange a rack in the middle.
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6
Coat a 12-well muffin pan with butter or line it with paper cupcake liners.
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7
Toss the rhubarb with 1/4 cup of the sugar in a medium bowl and let the mixture sit until the rhubarb releases some juice, about 5 minutes.
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8
Whisk together the flour, baking powder, baking soda, salt, and cardamom in a large bowl until evenly combined.
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9
Place the remaining 1/2 cup sugar, butter, egg, vanilla, and yogurt in a separate medium bowl and whisk until smooth.
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10
Add the wet ingredients to the dry and mix just until combined, about 25 to 30 strokes.
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11
Stir in the reserved rhubarb, about another 10 to 15 strokes.
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12
(The mixture will be thick.)
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13
Place a rounded 1/4 cup of batter into each muffin well (the wells will be full) and evenly sprinkle the streusel over top.
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14
Bake until a toothpick comes out clean, about 20 to 25 minutes.
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15
Place the muffin pan on a wire rack and let the muffins cool for 15 minutes in the pan.
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16
Remove the muffins from the pan and serve warm or let cool to room temperature.
