• Preheat your oven to 180°C (356°F)
• Peel and chop your apples into cubes.
• Place them in a saucepan with a splash of lemon juice (this will stop the apples from oxidizing).
• Cook them on low heat until they are softened (not mushy). Keep an eye on the pan and stir regularly to avoid sticking and burning.
• Let the apples cool off.
• Separate the egg yolks from the egg whites.
• In a large bowl, cream the egg yolks with the sugars.
• Add in the cinnamon, baking powder, baking soda, and salt.
• Pour in the melted butter and mix well. Make sure the butter has cooled off before adding it in, to avoid cooking the eggs.
• Add 1 cup of the dark rye flour and mix it in until well incorporated.
• In a separate bowl, whisk the egg whites to stiff peaks. Use an electric mixer for this.
• Fold in the whisked egg whites in the muffin butter. Use gentle folding motions to avoid losing that fluffy and airy texture.
• Add in the chopped apples and raisins. Mix them in gently.
• Now it's time to add the rest of the flour. I recommend you do this gradually as you might not need the whole amount of flour or need more than that. This depends on the flour you use, the size of the eggs, and the type of apples used in the recipe. The end result should be a normal muffin batter. Not too thin and runny, nor too thick and dry.
• Prepare your muffin tray with paper muffin cups (or reusable silicone ones).
• Add in the muffin batter. I recommend you fill them up halfway and then equally add up the rest of the batter. This way you make sure all the muffins are the same size.

Make the streusel (crumb topping):

• In a large bowl, mix in the brown sugar, cinnamon, dark rye flour, and cold butter.
• With your hands crumble all the ingredients together.
• This results in a clumpy, sand-like texture.
• Top the muffins with the streusel.
• Add it in gradually to ensure an equal spread on all the muffins.
• Bake the muffins at 180°C (356°F) for about 25 minutes. They should have risen well and be golden brown on top.
• Let the muffins cool off in the tin for about ten minutes or so. After that, you can remove them and place them on a wire rack to completely cool off.
• Serve and enjoy!