To prepare a Grandma Moyers rhubarb and strawberry coffee cake recipe, first you need to gather your ingredients. First, you'll need the following ingredients: 1 cup of sugar, 1 tablespoon of butter, 2 tablespoons of vanilla, and 1 teaspoon of salt. Then, preheat the oven to 350 degrees F (180 degrees C) and prepare the cake pan by lining it with parchment paper. Next, pour the batter into the prepared pan and bake it for 35 to 40 minutes, or until the top is browned and the center springs back when you touch it.