Oven temp of 350 degrees. Grease and flour a 12 cup bundt pan, cover all creases in bundt pan.
Need two bowls. In Bowl One, Mix dry ingredients, flour, baking powder, baking soda and salt. In bowl Two (larger bowl) beat butter, granulated sugar, on high for 2 to 3 minutes until fluffy. Beat in eggs one at a time. Whisk in 1/4 cup lemon juice, the zest, thyme and vanilla. On low speed mix in half the flour mixture, then buttermilk, then last of flour mixture. Pour batter into greased bundt pan. Tap to release air in batter.
Bake at 350 degrees for 50 minutes to 1 hour; until a toothpick in center of cake comes out clean.
Cool in bundt pan for exactly 10 minutes. Loosen edges with paring knife, turn out onto plate, gently shaking to remove, allow to cool completely.
In a bowl, mix confectioners sugar, cream and remaining lemon juice on low until combined. Drizzle over cake with spoon. Garnish with thyme sprigs if desired.