2 cups milk
2 eggs
1/2 cup granulated sugar (i found i needed a bit more for it to be sweet enough)
1/4 cup all purpose flour
2 tsp cornstarch
4 tsp butter
1/2 tsp lemon extract

(I’d also add in like, a teaspoon at LEAST of lemon zest. I don’t think you can substitute any of the milk for lemon juice, so zest is your best bet)

Heat milk in saucepan until bubbles form around edge. In a medium bowl, whisk eggs, sugar, flour, and cornstarch until smooth, gradually whisk in milk (this step is important to avoid clumps!!) Return to saucepan, cook over medium heat whisking just until thickened and bubbly (5 minutesish. STIR CONSTANTLY or it’ll burn)
Remove from hear, stir in butter, extract (and zest) refrigerate until firm.