Prepare a 9” cake pan by brushing with oil and lining the base & sides ( only the depth of the pan) with parchment. Preheat your oven to 335 and position the rack to be in the center for even baking.
In a medium sauce pan melt 2 oz. of butter (½ total volume listed above). Turn off heat and add in brown sugar, 1teaspoon vanilla and ground anise. Mix thoroughly to combine and pour into prepared cake pan.
Place half the raspberries in the center of the prepared cake pan. Choose thin spears of Rhubarb and cut into 1” angled slices measuring about 2-1/2” long. Begin placing in the brown sugar mixture, arranging around perimeter of the pan. Set aside.
In a medium size bowl sift together the flour, sugar, baking powder and salt. Toss with a metal spoon to combine all the ingredients.
In a small sauce pan melt the remaining 2 oz. of butter and add the milk to combine and slightly warm so the butter doesn’t coagulate. Remove from the heat and cool for 5 minutes. Add in the remaining 1Tablespoon of vanilla, amaretto and egg. Whisk to combine well.
With a medium heavy whisk begin adding the milk mixture into the sifted flour mix. Add slowly and look to dissolve most lumps. This should take no longer than 2 minutes. Take care to avoid lumps but not over mix.
Pour batter into prepared pan.
Bake for 30-35 minutes or until caramelized sugar is starting to bubble up the side of the pan. Test with a cake tester that the batter is cooked through, coming out clean when inserted into the center of the cake.
Let sit at room temperature for 5 minutes, and then place an inverted plate on the cake and invert. Take care to not get burned from the hot caramelized sugar.
Remove pan and peel off paper liner carefully. Let cool for 15 minutes. Serve with sweetened vanilla whipped cream and remaining fresh raspberries.