Preheat oven to 325 degrees (F).
Combine walnuts, cinnamon, and 1/4 cup sugar in a small bowl and set aside. This is the walnut filling.
Melt butter and coat a 14-x-10-inch baking pan. Layer 7 sheets of phyllo dough in the pan, buttering each sheet with a pastry brush.
Spread half of the walnut filling evenly over the top.
Layer another 7 sheets of phyllo dough in the pan, buttering each sheet.
Spread the remaining walnut filling evenly over the top.
Cover with remaining sheets of dough, buttering each sheet.
Bake for 40 minutes, then remove from oven and add the simple syrup over the top.
Allow baklava to cool completely before cutting it.*
While the baklava bakes, boil together the 1-1/4 cups sugar and 1 cup water for 10 minutes. Stir often until sugar dissolves in water. Add 1 teaspoon lemon juice.
Turn off flame and set syrup aside to cool. Pour cooled syrup on your baklava just as soon as it comes out of the oven.
If you don't have a 14-x-10-inch baking pan substitute a 9-x-13-inch casserole dish and trim an inch from the end of the phyllo sheet roll before using.
Store baklava at room temperature, covered with a tea towel, up to 5 days.
*I found it easier to cut the baklava into traditional diamond shapes before baking. Just don't cut all the way through to the bottom of the pan. After applying the simple syrup and allowing to completely cool, re-cut along the original lines to make sure the baklava easily removes from pan.
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