Ground the almonds in a food processor or with a mortar and pestle. Avoid grinding them too much. Go for medium-small pieces.
Place the sugar and 1 cup of water in a large pot over medium heat. Stir for sugar to melt.
Add the ground almonds and stir.
When the mixture starts to boil add the semolina, juice from the lemon and vanilla beans seeds. Stir well and remove from heat.
Add the eggs, one at a time while stirring well. The filling is ready. Set aside and prepare the phyllo.
Heat the oven to 350°F
Divide and cut the phyllo roll into five equal pieces.
Unfold only one of the rolls and keep the rest under a damp towel to keep them moist. Open up the roll and keep the phyllo sheets stacked on top of each other.Start with the one on top. Brush some melted butter on all the phyllo surface.
Place a full teaspoon of the almond filling approximately 2.5 inches (6 cm) in from the edge, centered.
Very gently, lift the upper left corner and fold down diagonally creating an isosceles triangle shape. You will have some extra phyllo hanging outside the shape. It will be folded with the next step.
Hold the triangle gently and fold up this time up, diagonally. Repeat the same sequence to fold the rest of the triangle.Place finished triangles on a parchment paper-lined baking sheets. Brush a tiny amount of butter on top of each triangle to keep them moist while you are folding the rest.
Bake for 20 minutes at 350 F°, or until triangles have a light golden color.
Sprinkle powdered sugar all over triangles. Enjoy!