Preheat oven to 500 degrees.
Combine streusel topping ingredients in bowl with fingers until you have pea-sized clumps.
In large bowl, whisk flour, salt, baking powder, cardamom, and chopped apple.
In third bowl, beat eggs with whisk, add sugar, milk, canola oil, and vanilla extract. Whisk well.
With fork, gently mix wet ingredients into dry. Mix until batter is just barely cohesive, do not overmix!
Grease 6-tin muffin tins or 12-tin muffin tin with butter. Fill each tin ¾ full. Crumble streusel topping over each tin.
Place muffin tin into hot oven, then immediately turn oven temperature down to 400 degrees. Bake 15-25 minutes, depending on how big your muffins are.
Take out when very lightly browning on edges and inserted toothpick comes out clean. Remove from tin after 5 minutes and set on cooling rack.