Steep:  Preheat oven to 375°F.  Line muffin tin with liners.  In a small saucepan, add milk and rosemary.  Over low heat bring the milk to just barely a simmer then remove from heat.  Let steep while preparing the other ingredients.

Mix:  In a large bowl, whisk together canola oil, honey, brown sugar, sour cream, vanilla, egg and egg yolk.  Remove the tea bags from the milk and whisk the milk into the mixture.  Add in the flour, baking powder and kosher salt.  Stir with a spatula or wooden spoon until combined.

Fill:  Fill muffin liners ¾ of the way.  If using parchment cups (see notes) fill to the top.

Crumble:  In a food processor, add the ingredients and pulse 5 to 8 times until butter is smaller than pea size and a crumbly texture.  If you do not have a food processor, this can be done with a pastry cutter or your fingers.  Sprinkle over each of the muffins.

Bake:  Bake muffins at 375°F for 20 to 25 minutes for ¾ filled muffins and 30 to 35 minutes for fully filled muffins, or until an inserted toothpick comes out clean.  Best to eat right away for crisp crumble topping.  Can be kept in an air tight container for 3 to 4 days, but crumble may soften.