Start by greasing your slow cooker insert with butter or cooking spray.
In a bowl, whisk together the all-purpose flour, yellow cornmeal, baking powder, baking soda, and salt until well combined.
Cream the softened butter and sugar together using a whisk or electric mixer until light and fluffy, about 3-5 minutes.
Beat in the eggs one at a time, then mix in the sour cream, grated lemon zest, vanilla extract, and lemon juice until smooth.
Gradually add the dry mixture to the wet ingredients, stirring gently until just combined. Fold in the poppy seeds.
Pour the batter into your prepared slow cooker and smooth the top with a spatula.
Cover the slow cooker and cook on low for approximately 2 to 2.5 hours or until a toothpick comes out clean.
Let the cake cool in the slow cooker for 10 minutes, then transfer to a cooling rack. Whisk together confectioners' sugar and a splash of lemon juice to create a glaze, and drizzle it over the cake.
