Preheat oven to 350 degrees F. Butter and flour a 9-inch cake pan or cast-iron pan.
For the Compote:
In a small saucepan, over medium heat, add rhubarb, sugar and water. Cook, stirring occasionally, until rhubarb has softened. Strain and reserve juice. Set rhubarb aside to cool while you make the rest of the cake.
For the Cake:
Cream butter and sugar together until smooth. Add eggs, one at a time, mixing well after each addition until batter is light and fluffy, then mix in lemon juice. Gently mix in the baking powder, salt, thyme and flour, being careful not to over mix.
Pour the batter into the prepared pan and smooth. Spoon the rhubarb compote over the top of the batter then, using a butter knife, swirl the compote through the cake batter, being careful not to scrape the bottom of the pan.
Drizzle 2 tablespoons of the reserved rhubarb compote juice over the top, sprinkle with the rest of the lemon zest, thyme and sugar.
Bake 25 minutes or until knife inserted in center of cake comes out clean.
Serve warm or room temperature. Enjoy with more of the rhubarb compote mixed with whipped cream or Greek yogurt, served on the side.
Notes: Also delicious just substituting fresh berries or sliced stone fruit for the rhubarb compote.