Preheat oven to 350°F. Line cupcake pan with liners.

Cook the sweet potatoes: Scrub the potatoes and pat dry. Use a fork to poke holes in the skin of each potato. About 7 time should be plenty. Place one potato on a microwave safe plate and microwave for 2.5 minutes, flip potato and microwave an additional 2.5 minutes. If the potato is not soft enough at this point continue microwaving in 30 second increments. Repeat with second potato. (You can also roast the sweet potatoes in the oven, but this will take about 45 minutes). Once both potatoes are cooked, cut each in half and set aside to cool.

Make the Pecan Streusel: In a medium bowl, mix together all ingredients until well combined. Set aside.

By now the sweet potatoes should have cooled enough to handle. Scrape the potato out of the skin, place in a medium bowl and mash with a fork or pastry cutter. Measure two cups and set aside.

In the bowl of your stand mixer fitted with the paddle attachment, mix together flour, sugar, baking powder, cinnamon and salt until combined.

Cut butter into one inch cubes. With the mixer on low speed add the cubes of butter one at a time and mix until you achieve a crumbled sand like texture.

Add the egg whites and continue to mix on low until incorporated.

With the mixer still on low speed slowly pour in the buttermilk.

Add the vegetable oil, vanilla and 2 cups mashed sweet potatoes and mix until fully combined.

Fill each cupcake tin 3/4 full then top with pecan streusel.

Bake for 18-20 minutes or until a toothpick comes out clean with just a few crumbs.

Let the cupcakes cool in the tins for about 5-10 minutes and then transfer to a wire rack to cool completely.