Preheat your oven to 350°F (175°C). Butter a 9x13-inch baking dish or line it with parchment paper.

Prepare the fruit. In a medium bowl, toss diced rhubarb, chopped strawberries, and strawberry gelatin. Set aside while you make the batter.

Make the cake batter. In the bowl of a stand mixer fitted with the paddle attachment, add the unsalted butter and cream until light and fluffy. Add the sugar and mix until combined. Add the eggs, vanilla, milk, and mix to incorporate well. Add the dry ingredients (flour, baking powder, baking soda, and salt) and mix until just combined.

Make the topping. In a small bowl, mix chopped nuts, brown sugar, cinnamon, flour, and melted butter until crumbly. Sprinkle evenly over the fruit.

Assemble the cake. Spread half of the cake batter in the bottom of the prepared baking dish. Top with half of the rhubarb mixture and then repeat with the remaining batter and rhubarb layer. Sprinkle the nut topping over.

Bake for 35-40 minutes, or until a toothpick inserted in the center comes out clean and the top is golden brown and crisp.

Cool for at least 30 minutes before slicing. Serve warm with a scoop of vanilla ice cream or cold with a dollop of whipped cream.