1. Preheat the oven to 350°F (177°C). Line a muffin tin with paper liners or lightly grease it.

Crumb mixture

1. Prepare the cinnamon crumb mixture. In a medium bowl, combine the brown sugar, flour, and cinnamon. Add the melted butter and mix with a pastry cutter or two forks until the mixture forms pea-sized moist crumbs. It's okay if some crumbs are larger. Cover the bowl with foil or plastic wrap and refrigerate this mixture until needed.

Muffin batter

1. In a large mixing bowl, whisk together the flour, baking powder, baking soda, and salt. Set this dry mixture aside. 
2. In another large bowl, use a handheld or stand mixer fitted with a paddle attachment to beat together the butter, applesauce, and sugar until smooth and creamy, about 2 minutes. 
3. Scrape down the sides and bottom of the bowl as necessary. Add the eggs and vanilla and mix on medium-high speed until well combined. Add the Greek yogurt and mix until combined. The mixture may appear lumpy, but that's okay. 
4. Gradually add the dry mixture to the wet ingredients, mixing on low speed until just combined. Stir in the almond milk until just incorporated. Avoid over-mixing; the batter should be thick.
5. Spoon the batter into the prepared muffin tin, filling the muffin cups about halfway. Sprinkle about 1 tablespoon of the crumb mixture evenly on top of the batter. 
6. Spoon the remaining batter over the crumb layer so that it is in the centre of the muffin. Then top each muffin with the remaining crumb mixture.
7. Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted into the top of the muffin comes out clean. You may need to adjust this baking time, depending on the size of your muffin pan. For mini muffins, start checking for doneness around 12 minutes. For jumbo minutes, they may not be fully baked until closer to 30-35 minutes. 
8. Once the muffins are baked, allow them to cool in the tin for about 10 minutes, then transfer them to a wire rack to cool completely.
9. Enjoy the muffins warm or at room temperature. The best way to store leftovers is in an airtight container at room temperature for up to 3 days or in the refrigerator for up to a week.