Streusel topped french Toast cupcakes with maple buttercream

I was extremely curious to taste these cupcakes, and for the Streusel on top, I had no idea what that was. Im not sure exactly what Streusel is but I think it's supposed to be crumbly (which mine wasn't); and the icing? I've still put the recipe here, but I didn't like the taste.

FOR THE STREUSEL:
1/2 cup packed brown sugar
1 tablespoon sugar
1/2 cup plain flour
1/2 teaspoon cinnamon
1/4 teaspoon salt
5 tablespoons cold unsalted butter

FOR THE CUPCAKES:
3 cups plain flour
2 cups  sugar
1 tablespoon baking powder
2 teaspoons cinnamon
1/2 teaspoon nutmeg
1 teaspoon salt
1 cup unsalted butter, softened 
1 cup sour cream
4 eggs
1 tablespoon vanilla extract

To make the streusel: 

1. In a large bowl, combine the brown sugar, sugar, flour, cinnamon, and salt. Mix the cold butter into the mixture by hand, squeezing the pieces in to mix it.

2. Cover and freeze while you prepare the cupcakes.

** If you’re not using the streusel right away, refrigerate it until ready to use.

To make the cupcakes:

 1. Preheat oven to 180 C. Line a muffin pan with cupcake liners; set aside.

2. In a large bowl, or the bowl of a standing mixer, whisk together the flour, sugar, baking powder, cinnamon, nutmeg, and salt. 

3. Add the butter, sour cream, eggs, and vanilla and mix well, until the mixture is smooth. Get rid of any remaining flour by stirring the mixture by hand, with a spatula.

4. Place three tablespoons of batter in each prepared baking cup. Divide the streusel evenly among the cupcakes, and sprinkle it on each one. Bake for 20 minutes, or until a toothpick inserted in the center comes out clean.

Maple Buttercream:

1 cup unsalted butter, softened
4 cups confectioners’ sugar
1 1/2 teaspoons vanilla
1/2 teaspoon salt
1/3 cup maple syrup
2 tablespoons  heavy cream

Beat the butter on high speed until light and fluffy. Beat in the sugar until combined. Stir in the vanilla, salt, and syrup. Add the heavy cream and whisk on high for 4 minutes.