Preheat oven to 350° F. Line an 8x8 glass dish with parchment paper and lightly spray with nonstick cooking spray. Set aside.
In large bowl, combine butter, sugar, flour, and vanilla extract until dough forms. Press evenly into the bottom of prepared dish. Set aside.
In another bowl, whip cream cheese. Stir in sweetened condensed milk. Scrape sides and mix again.
Add beaten egg, lemon zest, and lemon juice. Mix until mixture starts to thicken, 20-30 seconds. Scrape sides and mix again briefly.
Pour cream cheese mixture overtop cookie bottom and smooth the top.
Bake 20-25 minutes or until cheesecake is set completely. Cool to room temperature (may take up to an hour), then refrigerate for at least 2 hours.
Remove from refrigerator and cut into 16 squares. Separate the squares
Sprinkle the tops of each square with 1 teaspoon of sugar and spread around with finger to evenly distribute sugar.
Torch the tops until the sugar melts and turns an amber color. If you don't have a torch, place under the broiler.
Return squares to fridge until ready to serve.