1. Preheat the oven to 375°F. Lightly grease a standard 12-cup muffin tin; or line the tin with papers, and grease the papers.
For the crumb topping
2. In a small bowl, whisk together flour, sugar and cinnamon, add melted butter and stir with a fork until crumbly and set aside.
For the muffins
3. In a large bowl stir together flour, baking powder and salt, Gently fold about 2/3 of apricots, and toss them until all are coated with thin layer of flour.
4. In medium bowl mix sugar and butter until the mixture becomes fluffy.
5. Add the eggs, one by one and mix well. Add the yogurt, vanilla sugar and mix until combined.
6. Add the yogurt and egg mixture to the flour mixture. Stir just until combined.
7. Spoon batter into prepared muffin tins, using two spoons or an ice cream scoop, filling about 2/3 of each cup. Cover the batter with the remaining apricots and then cover the apricots generously with streusel topping.
8. Place them in the oven and bake about 20-25 minutes or until the toothpick inserted in the center comes out clean.
9. Cool for 5 minutes in the pan then remove muffins and cool on a wire rack.