Preheat oven to 350 degrees F.

Butter a 10-by-15-inch rimmed baking sheet and line it with parchment. Also butter dat parchment paper.

In a bowl, whisk together flour, cinnamon, ginger, and salt. In another bowl, whisk together melted butter, sugar, molasses, lemon zest and juice, and eggs. Mix the dry ingredients into wet ingredients until smooth. Spread batter evenly in prepared sheet.

Bake until cake is dry to the touch and edges begin to pull away from sheet, 12 to 14 minutes.

Let cool 5 minutes. Loosen edges with a knife; flip out on to cooling rack. Remove parchment. Let cool completely.

Transfer cake to a work surface and cut up for desired use, like some delicious ice cream sandwiches!