Preheat oven to 350°F. Grease a 2-pound loaf pan (9x5-inch) with butter and line the base and sides with parchment paper.

Add eggs, sugar, and vanilla extract to a large bowl and whisk until pale and light, approximately 1 minute. Add the greek yogurt and oil and whisk until thoroughly combined.

Sift flour, baking powder, and salt into the bowl with wet ingredients. Then add the ground Earl Grey tea leaves. Using a spatula, fold gently until a few streaks of flour remain.

Pour the batter into the prepared pan and bake on the center shelf for 50–55 minutes until golden brown, the sponge springs back, and a toothpick inserted into the center comes out clean. Cover cake with aluminum foil if it is browning too quickly. Cool cake in the pan on a wire rack for ten minutes, then remove from the pan to cool completely before glazing.

Combine the blue pea flowers and 1/2 cup water in a small pot and bring to a boil. Let it simmer for 5 minutes and the flower's color has leeched out. Strain the liquid and discard the flowers. In a bowl, mix the powdered sugar and yogurt, and a tablespoon of the blue coloring. If the glaze is too runny, add more powdered sugar, a tablespoon at a time, and mix until the desired consistency is reached.

Pour glaze over cooled cake and set aside for ten minutes to allow glaze to harden. Slice and serve.