Preheat oven to 350F/170C. Grease or place muffin papers inside 12 muffin tin.
To prepare streusel, in a medium bowl, combine brown sugar, apples, walnuts, flour and cinnamon. Stir in melted butter and set aside.
For the crumble; in a small bowl, add all the ingredients: butter, flour and sugar. And with your fingertips work the butter into the flour and sugar to form coarse crumbles. Set aside.
For the muffins, in a medium bowl, combine flour, baking powder and baking soda. Mix well. In a large bowl of standing mixer, set on medium speed and beat butter and sugar until light and fluffy (about 10 minutes).
Add eggs, one at a time, beat well after each addition. Add vanilla. Set mixer to low, alternately beat flour mixture and apple juice into egg mixture.
Spoon the batter into the 12 muffin tin and spoon on each muffin batter the streusel mixture, we prepared earlier. Bake for 15 minutes.
Remove the muffin tin from the oven, sprinkle the top with the crumble and bake for another 15 minutes. Transfer to wire rack and let cool completely before enjoying them.