Preheat the oven to 375 degrees Fahrenheit. Lightly grease a roughly 12 x 9-inch sheet pan , line the bottom with parchment paper, and set it aside.
Mix together the flour, almond meal, baking powder, cinnamon, ground ginger, and salt in a large bowl until combined. Set aside.
Beat the butter and sugar together in the bowl of a stand mixer fitted with the paddle attachment at medium speed until smooth and fluffy, about 1-2 minutes. Add the eggs, one at a time, beating well after each addition, then add both yolks at once and beat until smooth. Add the honey and vanilla extract and mix until combined.
Add half of the flour mixture and mix until partially incorporated, then add half of the milk and mix until smooth. Add the remaining flour mixture and mix until nearly incorporated, then add the remaining milk and mix until completely smooth.
Pour the mixture into the prepared pan. Lay the rhubarb stalks long-ways in the pan on top of the cake batter. Place the pan in the oven and bake until golden brown on top and a toothpick inserted into the cake comes out clean, about 45 to 50 minutes.
While the cake is baking, prepare the vanilla syrup. In a small saucepan, bring the sugar and water to a boil over medium heat. Remove from heat, stir in the vanilla extract, and set aside to cool.
As soon as you remove the cake from the oven, pour the syrup over it. Allow the cake to cool completely, then then sprinkle with the sliced almonds and powdered sugar. Serve immediately.