Preheat oven to 350°F (175°C). Line an 8×8 baking dish with parchment or lightly grease it.
Beat softened butter and sugar until light and fluffy, about 2–3 minutes.
Mix in the egg, vanilla, lemon juice, and zest until smooth.
Whisk flour, baking powder, and salt in a separate bowl. Gradually add to the wet mixture to form a soft dough.
Gently stir in blueberries and white chocolate chips without crushing the berries.
Spread dough in the pan. Bake 28–32 minutes until edges are golden and a toothpick comes out with a few moist crumbs. Let cool.
Melt white chocolate with coconut oil and drizzle over the cooled bars. Let set.
Cut into 16 bars. Serve at room temp or chill slightly for a firmer bite.