Set your oven rack to the middle of the oven. Preheat oven to 400 degrees F. Line a 12-cup muffin pan with cupcake liners or spray with non-stick cooking spray (I prefer to use cupcake liners to avoid over-browning the muffin bottoms).
In a medium bowl, whisk together the flour, baking powder, and salt.
Add the butter and sugar to a large mixing bowl and use an electric mixer to mix for 3 to 4 minutes, until light and fluffy. Add the eggs, one at a time, a beat until well combined. Add milk, lemon zest, lemon juice, and almond extract, and continue to mix for a minute or two until smooth.
Add half of the flour mixture and beat just until combined. Add half of the Greek yogurt and mix again, just until combined. Repeat with remaining flour mixture, Greek yogurt, and the poppy seeds, mixing just until combined and the poppy seeds are incorporated throughout the batter. Be careful not to overmix.
Divide the mixture between the prepared muffin cups. Sprinkle each muffin with ½ teaspoon sugar and then sprinkle with 2 teaspoon sliced almonds, using your fingers to very lightly tap the almonds on to the surface of the muffin batter.
Bake for 18 to 20 minutes or until edges are golden and a pick inserted in the center comes out clean. Remove the pan from the oven and allow the muffins to cool for 5 minutes before removing them from the pan to a wire rack to cool completely.