Preheat oven to 380°F. Line a cupcake tin with cupcake liners or spray with non stick baking spray. Make the streusel topping first: combine the flour, brown sugar, almonds (optional) and lemon zest in a medium sized bowl. Add the pieces of cold butter into the bowl and use a pastry blender or fork to cut the butter into the mixture until it is the texture of coarse meal. You do not want it to become a cohesive dough. Set aside.
In a large bowl, whisk the flour, sugar, poppyseeds, baking powder, baking soda, salt, lemon zest and cardamom together.
In a separate bowl, whisk the milk, butter, eggs, lemon juice and lemon extract together until smooth. Gently fold in this mixture (10-12 stirs) into the flour mixture until just combined. It will be very light and fluffy & it's OK if it's not all mixed.
Use a 1/4 cup measuring cup to scoop batter into each cupcake tin. Then top each muffin with about ~1 Tbsp. streusel topping. Place in oven and immediately turn the oven to 400°F (this helps ensure a dome on your muffins instead of flat muffin tops!) Bake for 15-17 minutes or until you insert a toothpick and it comes out clean. Enjoy!