1 stick (1/2 cup, 113 grams) unsalted butter at room temperature
1 cup (214 grams) granulated sugar plus 2 tsp for sprinkling
1 large egg, at room temperature
1 1/2 tsp vanilla extract
2 cups (256 grams) all purpose flour, saving out 1 Tbsp to toss with rhubarb
2 tsp baking powder
1 tsp salt
2 cups thinly sliced rhubarb
Set oven to 350F Lightly butter a 9×9 square baking pan. I like to line the pan with parchment paper with overhanging ends so I can easily lift out the cooled cake for cutting. That’s optional.
Stir the lemon juice into the half and half and set aside.
Cream the soft butter and sugar in a stand mixer, or with electric beaters, until fluffy and pale yellow. Beat in the egg and vanilla, scraping down the bowl as necessary.
Take 1 Tbsp of the flour to the rhubarb and toss well.
Whisk together the remaining flour, baking powder, and salt.
Add half of the flour mixture to the bowl and blend in. Add all of the half and half, and blend in. Finally add the rest of the flour and blend just until combined, don’t over mix. Fold in the rhubarb. Note: the batter is on the thick side.
Spread the batter into the prepared pan and sprinkle the top evenly with a little sugar. Bake for about 40-45 minutes, or until the cake is turning golden and a toothpick in the center comes out without wet batter clinging to it (moist crumbs are fine.)