• Preheat the oven to 360°F/180°C and line the muffin pans with paper liners.

Streusel:

• Make the streusel first by combining flour, brown and white sugar, and cinnamon in a medium bowl. Add the soft butter and rub it into the dry ingredients until coarse crumbs form. Chill until ready to use.

  1 ¼ cups all-purpose flour + ½ cup unsalted butter + ⅓ cup brown sugar + 3 tablespoons white sugar + ½ teaspoon cinnamon

Muffins:

• Prepare the apples: Peel, core, and dice the apples, then mix them with the lemon juice and set aside.

  1 cup diced apples + 1 tablespoon lemon juice
• Mix dry ingredients: Combine flour, both sugars, baking powder, cinnamon, and salt in a bowl.

  2 ½ cups all-purpose + ⅓ cup granulated sugar + ⅓ cup brown sugar + 2 ½ teaspoons baking powder + 1 teaspoon cinnamon + a pinch of salt
• Mix wet ingredients: In a large bowl, mix the eggs, oil, sour cream, and vanilla extract.

  2 large eggs + ⅓ cup neutral-tasting oil + ¾ cup sour cream + 1 teaspoon vanilla extract
• Fold ingredients together: Gently fold the dry ingredients into the wet ingredients without overmixing, then fold in the apples.
• Assemble: Divide the batter into the prepared muffin tins and sprinkle the streusel on top of each muffin.
• Bake the muffins for about 25 minutes until the streusel is golden and a toothpick inserted in the center comes out clean.

Glaze:

• Make the glaze: Mix the confectioner’s sugar with 1 tablespoon of lemon juice, adding a few more drops if needed to reach a thick paste.

  ½ cup confectioner’s sugar + 1 to 1 ½ tablespoons lemon juice
• Glaze the muffins: Drizzle the glaze over the muffins immediately after removing them from the oven.
• Cool the muffins: Let them rest in the pan, then transfer to a wire rack to cool completely.