Rhubarb Upside Down Cake

Rhubarb Upside-Down Cake
This is a GREAT cake! It's incredibly moist and tastes perfect with the rhubarb. The crunchy crumb topping is the perfect addition.

Crumb Topping
4 Tbls (55g) butter, melted
1/2 c (70g) flour
1/4 c (50g) sugar
1/4 tsp salt

Stir together all ingredients until moist and crumbly.

Butter Cake
3/4 c (175g) butter, room temp
1 lb (455g) rhubarb, trimmed and cut on a very sharp diagonal
1 3/4 c (350g) sugar
1 1/2 c (355g) flour
1 1/2 tsp baking powder
1 1/2 tsp salt
1/2 tsp orange zest
1 tbls fresh orange juice
2 eggs, room temp
1 c (240ml) sour cream

Preheat oven to 350F (175C).

Butter a 9-inch round cake pan (2 inches deep). Dot with 4 tablespoons (55g) butter (cut into pieces). Toss rhubarb with 3/4 cup (150g) sugar; let stand for 2 minutes. Toss again, and arrange in pan.

Whisk together flour, baking powder, and salt. Beat remaining 1/2 cup (110g) of butter and cup sugar with a mixer on medium speed until pale and fluffy. Beat in zest and juice. Beat in eggs, 1 at a time, until incorporated, scraping down sides of bowl. Beat in flour mixture in 3 additions, alternating with sour cream, until smooth. Spread evenly over rhubarb. Crumble topping evenly over batter.

Bake until a toothpick inserted into the center comes out clean and top springs back when touched, about 1 hour. Let cool for 10 minutes. Run a knife around edge of cake, and invert onto a wire rack. Let cool completely.