Preheat oven to 350°F (175°C). Grease an 8.5 x 4.5 inch loaf pan and line with parchment paper, leaving overhang on the long sides.
Place chopped dates in a heatproof bowl, sprinkle with 1 teaspoon baking soda, and pour boiling water over them. Let soak and cool for at least 15 minutes.
In a medium bowl, whisk together flour, baking powder, 1/2 teaspoon baking soda, salt, cinnamon, and nutmeg. Set aside.
Beat softened butter, granulated sugar, and brown sugar in a large bowl until creamy and light, about 2 minutes. Add egg and vanilla and beat until combined.
Pour the entire date mixture (dates and liquid) into the butter mixture and stir gently until combined.
Add the flour mixture to the wet ingredients and fold with a spatula until just combined. Do not overmix.
Gently fold in the chopped walnuts until evenly distributed through the batter.
Pour batter into the prepared pan and spread evenly. Tap the pan on the counter to release air bubbles.
Bake for 45-55 minutes, tenting with foil at the 30-minute mark if the top is browning too quickly. Bread is done when a toothpick comes out clean or the internal temperature reaches 200-205°F (93-96°C).
Cool in the pan for 15 minutes, then lift out using parchment handles and transfer to a wire rack. Cool completely, at least 1-2 hours, before slicing.