Preheat oven to 350 degrees F.
Line a 9 x 13 pan with parchment paper, leave some paper on each end so it's easy to lift the bars out when they set.
Melt butter in microwave, or over low heat on stove-top.
In a bowl combine the butter, cake mix, 1 egg, and 1 tablespoon meyer lemon juice and whisk until blended thoroughly. Divide the dough, and press ⅔ of it into the pan.
In a stand mixer combine the cream cheese, sugar and extract, beat until fluffy and well blended.
Add the other egg, lemon juice and zest to the mixer. Beat again till well combined.
Add the rest of the cake mixture to the bowl and mix briefly.
Pour batter over the crust, then top with blueberries.
Place the pan in the oven, and bake for about 45 to 50 minutes.
Remove from oven and cool completely.
Place in the fridge and let set for about an hour.
Remove the pan from the fridge and use the parchment to lift the bars from the pan.
Cut into squares.
Serve with a big old thank goodness I didn't have to juice the lemons smile!