Preheat oven to 350°F (180°C). Lightly spray a tall-sided 8-inch round cake pan with cooking spray. Line bottom of pan with a slightly damp sheet of parchment paper. (This helps prevent the marmalade from burning.)
In a small bowl, place ground tea.
In a small saucepan, bring milk to a boil over medium-high heat. Pour hot milk over tea to bloom and bring out its flavor.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter, caster sugar, and lemon zest at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition.
In a medium bowl, stir together flour and baking powder. Fold flour mixture into butter mixture. Add warm Earl Grey milk, quickly stirring into batter.
Spread all but a few tablespoons marmalade in prepared pan. Spread batter over marmalade.
Bake until pudding springs back when touched in center, 35 to 45 minutes. Let cool in pan for 5 minutes; carefully invert onto a serving plate.
In another small saucepan, heat remaining marmalade over medium heat. Spread over top of cake. Serve warm with Vanilla Custard.
Notes
*We used King Arthur Cake Flour and Wilkin & Sons Tiptree Orange Medium Cut Marmalade.
*If you're using granulated sugar, measure by weight.
Recipe by Bake from Scratch at https://bakefromscratch.com/marmalade-pudding/