In a large bowl with a stand or hand mixer, blend sugar and butter together until light and fluffy, about 3 minutes. Then add vanilla, 1 egg and orange juice and combine. Then add flour, baking powder and salt and mix with fingers or spoon until just combined. Dough should be slightly sticky. Form dough into a ball, wrap in plastic wrap and chill overnight.
Meanwhile, make the filling. Mix together tahini paste and powdered sugar to desired level of sweetness. If tahini is a little dry, add water until the mixture is easy to combine and is about the consistency of peanut butter.
Preheat oven to 350 degrees F. On a lightly floured surface, roll dough out to about 1/8” thickness, then cut into circles with a 3 or 3 1/2-inch round cookie cutter or a wine glass. Place 1 teaspoon filling at center of dough circle and fold over the three corners to form a triangle.
Place hamantaschen on a parchment lined cookie sheet and freeze for 30 minutes to prevent spreading. Using a pastry brush, brush with egg wash and sprinkle with sesame seeds. Bake for 12-15 minutes until browned on the bottom. Cool completely on a rack before serving.