For the crust, whisk together the flour, gum, salt and baking powder. In another bowl cream together the butter and sugar for 2 minutes. Stir in half of the flour mixture, then add in the egg yolks one at a time, mixing well after each. Add remaining flour, mixing until dough comes together. Press into a greased and parchment lined 9x9” baking pan. Bake at 350°F for 15 minutes until light golden brown. Set aside to cool.

For the filling, combine all ingredients, mixing until smooth and thick. Spread evenly over cooled crust.

For the topping, beat the egg whites with the lemon juice until foamy, then slowly add in sugar. Once stiff peaks form, spread meringue over filling and bake for another 15 minutes.

Cool at least 20 minutes then use a knife dipped in hot water to cut into squares.